Photographs inducJed in the origiDal mamwript have been leploduc:ed ...... Guerrero terrane and Sierra Madre Oriental that could have provided channels for ...
INFORMATION TO USERS This mannscript pas been repzLduced from the microfilm master. UMI films the text directly from the origiDal or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any ~ of wwputer primer. 'I1Ie qaaIity 01 dais reprududioD is cJrpn+et apeD the quality or the copy sgJppiUed Broken or iDdistinct prim, colored or poor quality iIlusttaticms and photosraphs, prim bleedtbrough, subs"h"ani margins, and imploper alignment can adversely affect Ieploducticm
In the UJ]like1y. evem tba.t the author did not send UMI a complete mamscript and there are missing pages, these will be noted. Also, if UDailduized copyright material had to be IClllOiicd, a DOte will jndjcate the ddetioD..
Oversize materials (e.g., maps, chawiDgs, charts) are reproduced by secticmiDg the original. begi""ing at the upper left-hand corner and Wi II j''''i.tg from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs inducJed in the origiDal mamwript have been leploduc:ed xerographically in this copy. Higher quality fI' x 9" black and white photographic prints are available for any photographs or illustrations appeariug in tbis copy for an additioual charge. Contact UMI directly to order.
UMI A Bell & Howell Information Company 300 North Zeeb Road. Ann Art:Ior. MI4810S-1346 USA 313!761-4700 8OQ:52H)6OQ
-------------
--
1
THE VOLCANOGENIC MASSIVE SULFIDE AND SEDIMENTARY EXHALATIVE DEPOSITS OF THE
GUE~qERO
TERRANE, MEXICO
Miguel Angel Miranda Gasca
Copyright
~
Miguel Angel Miranda Gasca 1995
A Dissertation Submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of
DOCTOR OF PHILOSOPHY
In the Graduate College THE UNIVERSITY OF ARIZONA
1 9 9 5
OMI Number: 9531108
Copyright 1995 by Miranda, Gasca Miguel Angel ~1 rights reserved.
0Mcr Microfor. 9531108 Copyright 1995, by UMI Company. All rights reserved.
This .icrofora edition is protected against unauthorized copying under ~itle 17, United States Code.
UMI 300 Borth Zeeb Road MI 48103
Ann Arbor.
2 THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
As members of the Final Examination Committee, we certify that we have Miguel Angel Miranda Gasca read the dissertation prepared by______________________________________ __ entitled __-::T~h:.:.e==_...::v:....:o:::..l=c~a~n.:..:o:::..g=e::.:n~l.::;.·c==_.:.:m~a~s=s:..::i:...;v:...;e==_..::s~u::..:l=f..:i..::d:..:e=__:::a:.:.n:..::d=__:::s..::e:.::d::..:l.::.:·m=e;.:.n.:.:t::.;a=r....ly~_ exhalative deposits of the Guerrero Terrane. Mexico
and recommend that it be accepted as fulfilling the dissertation of Philosophy
Date Date
Fernando Ortega Date
Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement.
ii?~«LG~
Dis~ion Director
Spencer R. Titley
Date
3
STATEMENT BY THE AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to the borrowers under rules of the library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgement of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part y be nted by the copyright holder. SIGNED: ______~~~~~--------~~-------
--------
. . .-
- ---------------
4
ACKNOWLEDGEMENTS The Consejo Nacional de Ciencia y Tecnologia (CONACyT), Mexico, awarded this writer a scholarship for studies at the University of Arizona from 1990 to 1994 and made it possible to carry out this research. This dissertation would not have been possible without the generous funding for field and laboratory expenses provided by BHP Minerals through John E. Larson and Philip Pyle. I benefitted from the expertise, guidance, and discussions with my advisor Spencer R. Titley. The members of my dissertation committee P. Coney, P. Damon, J. Ruiz, J. Larson, and F. Ortega were very helpful during the development of this work. C. Eastoe enhanced my understanding of volcanogenic sulfide deposits and analyses of sulfur isotopes. V. de la Garza, Exploration Vice President of Industrias Penoles, permitted me to carry out field work on the Penoles properties and provided logistical support. G. Garcia, resident geologist at Rey de Plata and later at Tizapa, discussed the geology of these deposits and provided ~aterials. R. Tellez, Manager of Penoles Toluca office shared his knowledge on the stratabound deposits of Michoacan with the author and provided logistical support during his stay at Mexico and Michoacan States. F. Ortigosa and R. Padilla introduced me to the geology of La Minita, Michoacan and Cuale, Jalisco. I am thankful to A. Gomez and C. Macias of Instituto de Geologia, UNAM, and R. Merida and J. Parga of Consejo de Recursos Minerales who kindly introduced me to the geology of the Francisco I. Madero and Guanajuato deposits. I. Paterson, COMINCO Exploration Manager, and V. Espinosa, pe~itted me to visit the El Bramador deposit. A. Castaneda allowed field work at the La America Mine of Talpa, and provided information of his property. M. Franco S. and F. J. Langarica P. were very helpful during field work at La America and EI Rubi of Talpa, Jalisco. R. Martine= and G. Arreola permitted me to work on Industrial Minera Mexico property Calmalli. Baja California. J. Chanfreau, Tepmin, S.A. manager, allowed the author to collect samples from the La Testera Mine, San Antonio, Baja California. Ing. M. Arzate from Minera EI Porvenir de Zacualpan provided samples for this work. G. Mercado shared knowledge and samples of Apaxtla, Guerrero. J. Nunes, consejo de Recursos Minerales Michoacan Resident, J. Librado, and J. Bustamante discussed the geology of Arroyo Seco, Michoacan, with the writer and provided samples and maps. o. Talavera collaborated in some calculations. I thank J. Ramirez for the discussions on the tectonic evolution of the Guerrero Terrane. This dissertation is dedicated to my wife Leandra and to M6nica, Catalina, and Omar.
----------
5
TABLE OF CONTENTS Page ABSTRACT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . • . . . . . . . . 13 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 GENERAL DESCRIPTION OF THE GUERRERO TERRANE . . . . . . . . . . . . . . 21 VOLCANOGENIC MASSIVE SULFIDE AND SEDIMENTARY EXHALATIVE DEPOSITS OF THE GUERRERO TERRANE . . . . . . . . . . . . . . . . . . . . . . . . . 40 General Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Volcanogenic Deposits of the Teloloapan Subterrane .... 43 Rey de Plata, Guerrero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Local geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Host rock geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Ore bodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Tehuixt la body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Rey de plata ore body . . . . . . . . . . . . . . . . . . . . . . . . 78 Other sulfide lenses . . . . . . . . . . . . . . . . . . . . . . . . . 79 Fluid inclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Chlorite geochemistry . . . . . . . . . . . . . . . . . . . . . . . . 82 Sulfur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Campo Morado group, Guerrero . . . . . . . . . . . . . . . . . . . . . . . 91 Reforma Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Sulfur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Azulaquez group, Guerrero . . . . . . . . . . . . . . . . . . . . . . . . . 100 Aurora II, Guerrero . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Campo Seco, Guerrero. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Tizapa-La Esmeralda group, Mexico . . . . . . . . . . . . . . . . . 105 Tizapa, Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 La Esmeralda, Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Volcanogenic Deposits of the Zihuatanejo Subterrane .. 115 Cuale-El Bramador group, Jalisco . . . . . . . . . . . . . . . . . . 115 Cuale, Jalisco . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 EI Bramador, Jalisco . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 La America, Jalisco . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Sulfur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 EI Rubi, Jalisco . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Sulfur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 EI Desmoronado, Jalisco . . . . . . . . . . . . . . . . . . . . . . . . 148 La Minita, Michoacan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Las Ollas Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Copper King, Guerrero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Sulfur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Arteaga Complex . • . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . 163
---
----
-- -----------------
6
Arroyo Seco, Michoacan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Sulfur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 Northern Guerrero Terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 Francisco I. Madero, Zacatecas . . . . . . . . . . . . . . . . . . . . 173 Stratabound Mineralization . . . . . . . . . . . . . . . . . . . . . 175 Correlat ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 SuI fur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Guanaj uato group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 San Ignacio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Yolanda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Arroyo de Cata (La Virgen 0 EI Muerto) ......... 185 Sulfur isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Baja California Portion of Guerrero Terrane . . . . . . . . . . 186 Calmalli, Baja California . . . . . . . . . . . . . . . . . . . . . . . . 188 MASSIVE SULFIDE CHEMISTRy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 SULFUR ISOTOPE STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
0 • • • • •
212
LEAD ISOTOPE STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 DISCUSSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 APPENDIX A: SUMMARY OF THE MAIN GEOLOGICAL CHARACTERISTICS OF VOLCANOGENIC MASSIVE SULFIDES AND SEDIMENTARY EXHALATIVE DEPOSITS OF THE GUERRERO TERRANE . . . . . . . . . . . . 247 APPENDIX B: CHEMICAL ANALySES . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
__
-
00-
___ -
_ _ _ _ _ _ _ _ _ _ _ _ _ _ __
7
LIST OF FIGURES Figure
Page
1 Tectonostratigraphic terranes of Mexico ............ 22 2 Guerrero subterranes of central Mexico ............. 23 3 stratigraphic columns of southern Guerrero terrane.3l 4 Stratigraphic columns of northern Guerrero terrane.32 5 Tectonic model of southern Guerrero terrane ........ 37 6 Tectonic model of central Guerrero terrane ......... 38 7 Guerrero terrane tectonic model .................... 39 8 VMS and SEDEX deposits of Guerrero terrane ......... 41 9 Tonnage of VMS and SEDEX deposits of Guerrero terrane ............................................ 42 10 Tertiary and Mesozoic deposits of part of Teloloapan subterrane .............................. 47 11 Geologic map of Teloloapan-Rey de Plata region ..... 48 12 Palinspastic model of Teloloapan subterrane ........ 51 13 Rey de Plata district. Northeast-southwest crosssect ion ............................................ 52 14 Textural variations of sulfide ores of Rey de Plata deposit ...................................... 55 15 Nor.malized rare-earth diagram for Teloloapan subterrane and Rey de Plata andesite and basalt ... ~60 16 Normalized chondrite rare-earth diagram of Teloloapan subterrane and Rey de Plata rhyolite .... 61 17 Diagram of lithophile elements normalized with respect to MORB for basalt and andesite of Teloloapan subterrane and Rey de Plata ............. 63 18 Lithophile elements normalized against ORG of Teloloapan subterrane and Rey de Plata rhyolite .... 64 19 Plan of the central portion of Rey de Plata district ........................................... 65
8
20 Tehuixtla body, cross-section A-A' ................. 67 21 Tehuixtla body, cross-section B-B' ................. 68 22 Drill-hole TX-6, Tehuixtla body .................... 71 23 Drill-hole TX-24, Tehuixtla body ................... 73 24 Drill-hole ANT-17, Antares body .................... 74 25 Stratigraphic sections measured in the underground workings, Rey de Plata deposit ......... 76 26 Libra and Antares bodies, cross-section C-C' ....... 80 27 Homogenization and melting temperatures of fluid inclusions, Rey de Plata deposit ............. 83 28 Melting versus homogenization temperatures diagram, Rey de Plata deposit ............................... 88 29 Rey de Plata, Guerrero, 6'~s histogram ............... 86 30 Rey de Plata, Guerrero, Tehuixtla body. Vertical variation of 6:~S .......................... 87 31 Campo Morado group, Guerrero ....................... 93 32 Textural variations of Campo Morado deposit ........ 95 33 Drill-hole G-XC3-1-N30:E-10, Campo Morado, Guerrero ........................................... 98 34 Campo Morado 6'·s vertical variation. Overturned section, as described in text ...................... 99 35 Azulaquez group, Guerrero ......................... 101 36 Aurora II and El Salitre 6;'s histogram ............ 103 37 Campo Seco, Guerrero, stratigraphic section ....... I04 38 Campo Seco and Tizapa textural variations ......... 106 39 Campo Seco, Guerrero, 6 14 s histogram ............... 108 40 Tizapa group, Mexico .............................. 1l0 41 Schematic tectono-stratigraphic column for the pre-Tertiary rocks of the Zacazonapan-Tejupilco (Tizapa) area ..................................... lll
9
42 Schematic cross-section of Tizapa deposit ......... 112 43 Cuale-EI Bramador group, Jalisco .................. 116 44 Stratigraphic column of Cuale District ............ 117 45 Composite stratigraphic section of Cuale district.118 46 Geologic map of Cuale district .................... 120 47 Cross-section of Naricero body, Cuale district .... 121 48 Cross-section of the Socorredora body, Cuale, Jalisco. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 123 49 Cross-section of Coloradito body, Cuale district .. 124 50 Cross-section of Minas del Oro or Grandeza, Cuale district .................................... 125 51 6:'';s histogram for Cuale values .................... 127 52 Location of El Bramador VMS deposits .............. 128 53 Idealized stratigraphic column of El Bramador area .............................................. 129 54 EI Bramador and La America textural variations .... 131 55
6'~s
histogram for EI Bramador area ................ 133
56 La America geological map ......................... 134 57 Stratigraphic column and mineral and metal profiles through La America, Jalisco .............. 137 58 La America 6 3;s histogram .......................... 138 59 Vertical variation of 63~S values. La America, Jalisco ........................................... 140 60 Cross-section of El Rubi deposit .................. 142 61 ocotitlan VMS cross-section ............. , ......... 144 62 Stratigraphic section and chemical profiles of Ocotitlan VMS, El Rubi district ................... 145 63 El Rubi and Copper King textural variations ....... 146 64 6';s histogram. El Rubi, Jalisco ................... 149
10 65 Composit stratigraphic section of El Desmoronado district, Jalisco . . . . . . . . . . . . . . . . . . . . . 150 66 Structural section of El Desmoronado district, Jalisco . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 67 La Mini ta geological map . . . . . . . . . . . . . . . . . . . . . . . . . . 153 68 Structural section of La Minita, Michoacan ........ 154 69 Composite stratigraphic section of La Minita, Michoacan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 70
&~'S
histogram for La Minitc, Michoacan ............ 158
71 Copper King geological map . . . . . . . . . . . . . . . . . . . . . . . . 160 72 Copper King stratigraphic section and chemical profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 73 Copper King 6;;s histogram . . . . . . . . . . . . . . . . . . . . . . . . . 164 74 Vertical variation in 6 3 ·s, Copper King, Guerrero .. 165 75 Arroyo Seco stratigraphic column . . . . . . . . . . . . . . . . . . 166 76 Cross-section N75:E, looking to the northwest. Arroyo Seco, Michoacan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 77 Arroyo Seco, Michoacar., and San Ignacio (SI) and La Virgen (LV), Guanajuato textural variations .... 169 78 6 c ,s Histogram. Arroyo Seco, Michoacan . . . . . . . . . . . . . 172 79 Francisco I. Madero stratigraphic column .......... 176 80 Francisco I. Madero textural variations ........... 177 81
6~' S histogram. Francisco I. Madero, Zacatecas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
82 Guanajuato group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 83 San Ignacio and Arroyo de Cata or La virgen area geologic map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 84 San Ignacio cross-section . . . . . . . . . . . . . . . . . . . . . . . . . 184 85 6 3 ;s histogram. San Ignacio, La Virgen or Arroyo de Cata, and Yolanda, Guanajuato . . . . . . . . . . . . . . . . . . 187
11 86 Calmalli, Baja California cross-section ........... 189 87 Ternary plot of VMS and SEDEX deposits of Guerrero terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 88 Cu-Pb-Zn compositional field (Large, 1992) of Guerrero terrane VMS and SEDEX deposits . . . . . . . . . . . 193 89 Ag versus Pb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 90 Ag versus Zn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 91 Ag versus Cu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 92 Au versus Pb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 93 Au versus Zn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 94 Au versus Cu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 95 Au versus Ag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 96 Au versus pb+Zn+Cu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 97 Au versus Pb+Zn+Cu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 98 Ag/Au versus Zn+Cu+Pb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 99 Pb versus Pb+Cu+Pb . . . . . . . . . . . . . . . . . . . . . . . . . . . . ' . ' .207 100 Zn versus Zn/Zn+Cu+Pb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 101 Cu versus Cu/Zn+Cu+Pb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 102 Pb/Zn+Cu+Pb versus Zn/Zn+Cu+Pb . . . . . . . . . . . . . . . . . . . . 2l0 103 Ternary diagrams of compositions of VMS deposits of Guerrero terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 104
~:;S
for VMS and SEDEX of Guerrero terrane ......... 213
105 Pb/Zn+Cu+Pb versus
~J~S
0100 . . . . . . . . . . . . . . . . . . . . . . . 215
106 Zn/Zn+Cu+Pb versus
~3~S
0/00 . . . . . . . . . . . . . . . . . . . . . . . 216
107 Cu/Zn+Cu+Pb versus
~JIS
0100 ••. ............•....... 217
108 Ag/Au versus
~3~S
0100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
109 ::-Pb/::;Pb versus 20EPb/ 201 pb data for Guerrero terrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
12 110 Lead isotope data for Guerrero terrane showing samples from Tertiary deposits .................... 221 III Mesozoic Pb isotope data of rocks of the Guerrero terrane .................................. 222 112 Location of Selected Tertiary deposits of Guerrero terrane .................................. 223
LIST OF TABLES Table
Page
1
Metal production from Mesozoic stratabound deposits of the Guerrero terrane ................. 16
2
Principal lithological and chemical characteristics of the Guerrero subterranes ...... 24
3
Principal lithological and chemical characteristics of the Guerrero terrane basement.28
4
Reserves and geochemical character of the Guerrero terrane VMS and SEDEX deposits ................... 44
5
Mineralogy of the Guerrero terrane VMS and SEDEX deposits ......................................... 46
6
Reserves of the Tizapa deposit .................. 113
7
Grade and tonnage of the Calmalli deposit ....... 190
13
ABSTRACT More than 60 volcanogenic massive sulfide and sedimentary exhalative deposits are located in the composite upper Jurassic-lower Cretaceous Guerrero terrane of western Mexico. The deposits range from less than 100,000 metric tons up to 6 million of metric tons. Most of the deposits are Zn-Pb-Cu Kuroko type and are located within the Zihuatanejo and Teloloapan subterranes. The Guanajuato and Calmalli, Baja California, deposits are Zn-Cu. The Cu type Coppe~
King, Guerrero, deposit is located in the Papanoa
complex. Arroyo Seco, Michoacan, located in the Arteaga Complex, is the only Pb-type and can be classified as a sedimentarJ-exhalative deposit. The sulfides lenses have s~ffe~ed
metamorphism. The
6~~S
values of Teloloapan
deposits are mainly negative. The mean
63~S
values of the
deposits of Zihuatanejo subterrane are mainly positive. Lead isotopic data suggest that the source of metals for the Zihuatanejo, Teloloapan and Huetamo Tertiary epigenetic deposits of the Guerrero terrane was a combination of metal sources e.g. the Mesozoic crust, the middle-Tertiary volcanic rocks, and the Sierra Madre Oriental. Guanajuato, Zacatecas, Fresnillo, and Real de Angeles districts are located at the suture zone between Guerrero terrane and Sierra Madre Oriental that could have provided channels for hydrothermal systems that extracted metals from different sources.
14
INTRODUCTION More than 60 volcanogenic massive sulfide (VMS} and sedimentary exhalative deposits (SEDEX) are located in the composite upper Jurassic-lower Cretaceous Guerrero terrane (GT) of western Mexico. Their main characteristics are poorly known. The base and precious metals production of the Mesozoic syngenetic deposits has been low compared to the production of Tertiary epither.rnal and mesothermal worldclass districts of the same terrane such as Guanajuato, Zacatecas, Fresnillo, and El Oro. There is a close spatial association between the Mesozoic stratabound and the Tertiary mineralization. The Mesozoic stratabound and Tertiary mineralization are located in the same portions of the Guerrero terrane and are generally hosted in the same volcanic and sedimentary rock units. The metallic assemblages of both Mesozoic and Tertiary deposits are similar in each of the subterranes where they occur. The Guerrero terrane has been interpreted as an island arc floored by oceanic and continental crust. Other associated tectonic environments such as marginal basins have been recognized (Tardy et al., 1991). The direction of subduction that produced the arc(s) is matter of controversy; Coney (1983) and Tardy et ale
(1991) have
proposed westward subduction, Campa and Ramirez (1979) proposed eastward subduction and Ramirez et ale (1991) proposed two subduction zones, one to the east and one to
15 the west. The VMS and SEDEX deposits are clustered in areas of different litholcgy and tectonic setting of the Guerrero terrane. Four groups of deposits are present in the States of Guerrero and Mexico: The Campo Morado-Suriana, Azulaquez, Tizapa, and Rey de Plata. Another group of deposits is located in western Jalisco, around the Cuale deposit. Scattered occurrences are found in Zacatecas, Guanajuato, and Michoacan. Only some of the VMS deposits have been brought into production. Cuale, Jalisco, operated by Compania Fresnillo, a subsidiary of Penoles produced mainly Ag from oxidized ores during the last century, and base metals, Ag and Au from the sulfide zones from 1978 to 1992 (Table 1). La Minita deposit produced barite in a small operation during the 1950's and started larger production under Penoles Company during the late seventies. At the present time, the mine is being shut down. Tizapa, Mexico was discovered during the late 1970's and will produce in the near future under Penoles Company direction. Some other deposits have produced Au and Ag from the oxidized superficial zones mainly during late 1800's and early 1900's. This is the case of Cuale, and El Rubi, Jalisco, Campo Morado, El Faisan, and Suriana, Guerrero, Santa Rosa, Mexico, and Calmalli and Cedros Island, Baja California.
Table 1. Metal production from Mesozoic stratabound deposits of the Guerrero terrane (Metric tons).
DISTRICT AND MINE
PERIOD
PRODUCED METAL TONNAGE
CUALE (1)
Until 1984 (5) Total, until 1992
AMALTEA (2) CAMPO MORADO Reforma Mine SURIANA (4)
OX/SULF
GRADE Zn% Pb% Cut Ag ppm Au ppm
771,200 t 1,500,000 t
Sulfides Sulfides
4.9 1.7 0.4 4.8 1.3
156 169
0.6 1.15
266,500 t
Sulfides
13.6 2.6 1.0
154
1.0
(3)
1903-1913
XIX Century Before 1940
BARITA DE APATZINGAN La Blanca (6)
125,229 kg Ag 3,887 kg Au 250,000 t 300,000 t 225,000 t
Oxides Oxides Oxides
900-1500 574 7.0
4.6 0.4 0.2
50
0.5
LA MINITA
References 1 and 2.- Berrocal and Querol, 1991; 3.- Fl6res, 1933; 4.- Peftoles, 1987; 5.- Consejo de Recursos Minerales, 1993; 6.- Velasco, 1976.
....
0\
17
Purpose A purpose of this dissertation is to determine and compare the chemical, mineralogical, stratigraphic, and structural characteristics of the main VMS and SEDEX ores that occur in the Guerrero terrane. The comparison of similarities and differences of these ore-bodies will characterize a group of stratabound deposits that remains largely unknown. The determination of the characteristics of the stratabound deposits will contribute in the elucidation of the hydrothermal processes that produced them and on the tectonic and lithologic settings in which they developed. Tertiary epigenetic precious and base metal deposits are located in the same subterranes where the VMS and SEDEX ores occur. A second purpose of this investigation is to dete~ine
the role of Mesozoic rocks and their associated
s~ratabound
mineralization in the origin of the epigenetic
Tertiary deposits which are hosted in the same rocks.
Methodology Representative deposits were chosen for study from a bibllographic compilation by the author of known VMS and SEDEX deposits of the Guerrero terrane. Field work was carried out during the
s~~er
and December of 1991, March of
1992, summer of 1992, and March of 1993. Some deposits were
found not to be VMS or SEDEX, and the original list was :r.cdi f ied.
-
--------
18 Emphasis was placed on determining stratigraphic relationships of each deposit. Drill-core was sampled and described when it was available. Hosts rocks were milled in agate mortar and analyzed by XRAL, Ann Arbor, Michigan. Major oxides, Ba, Cr, Nb, Rb, Sr, and Zr were analyzed by XRF on compressed powders. Rare-earth elements, Th, U, and Y were analyzed by ICP/MS, and Mn by DCP. The detection limits, methods, and digestion procedures are shown in Appendix B. The sulfide samples were analyzed by ICP/MS by American Assay Laboratories.
T~e
Zn content above 10% was analyzed by
atomic absorption. Gold was analyzed by fire assay by the same laboratory. Analyses of sulfide, sulfate, and chlorite minerals were done by the author on a Cameca (Camebax) SX50 electron microprobe at the Department of Planetary Sciences of the University of Arizona. For Fe, Cu, Zn, Pb, and S in sulfide minerals the analytical conditions were 15 kV accelerating voltage, 20 nA sample current, and for As, Se, Sr, Au, Mn, Ag, Cd, Sn, Sb, Te, Ba, and Bi, the analytical conditions were 15 kV accelerating voltage and 80 nA sample current. Chlorite minerals were analyzed for B, Mg, Si, AI, Mn, Fe, and Ni with the analytical conditions 15 kV accelerating voltage and 20 nA sample current. Fluid inclusion measurements were done on a SEG Inc.adapted USGS gas flow heating-freezing stage calibrated
19 using Syn Flinc synthetic fluid inclusions. The precision of heating and cooling is ±1.4 at 374=C and ±0.1°C at O.oeC. Petrography was performed on polished and regular thin sections under a polarizing microscope. Several minerals were identified by X-ray diffraction on a Siemens D-500 Xray diffractometer with the following conditions: 30 mA, 40 kV, Cu target, 2 degrees 2 thetal minute, scintillometer 964 V, and graphite monochromater filter. Sulfur isotopes were determined on mineral separations made by hand picking under a stereoscopic microscope or by panning. Sulfide minerals were converted to SO: by combustion at 950°C with Cu:O (Robinson and Kunabe, 1975). Sulfates were converted to SO: by combustion with Cu 20 at 1,100 °c (Coleman and Moore, 1978) and CO 2 and H:O were separated by high vacuum distillation. SO: was measured on a modified VG602C mass spectrometer.
63~S
0100 are reported
with respect to Canon Diablo troilite international S isotope standard. Two in-house standards were analyzed along with two unknown samples. These standards were tested against standards of the Department of Scientific and Industrial Research, New Zealand, and the Ontario Geological Survey. Lead isotopes were analyzed by Geochron Laboratories of Cambridge, Massachussets, in a VG sector 54 mass spectrometer. Galena and other sulfide minerals were hand picked under a stereoscopic microscope and dissolved in aqua
20
regia. The Pb was isolated as
PbCl~
and
~~rified
by standard
HBr ion exchange procedures. The analytical error is better than ±O.05% including all type of errors.
- -- -_._-
------------------ -
21 GENERAL DESCRIPTION OF THE GUERRERO TERRANE
The Guerrero terrane (GT) was originally defined as a composite tectonostratigraphic terrane by Campa and Coney (1983). This is the largest terrane of Mexico and is located i~
the northwestern, central and southern parts of the
country (Fig. 1). The GT was subdivided in three subterranes of
Jurassic to mid-Cretaceous age: The Teloloapan-
la~e
:xtapan, Zihuatanejo, and Huetamo subterranes (Campa and CQne~',
1983). The southern and central portions of the GT
have been further divided into Hue~a~c,
al.,
Las Ollas, Zihuatanejo,
Arcelia, and Teloloapan subterranes (Ramirez et
~991;
Talavera et al., 1993). Other regions where the
G7 has been identified are Fresnillo, Guanajuato, Arperos, Sina:oa, and Baja California (Fig.2). The GT overlies d:tte~en~
types of basement in Arteaga, Placeres del Oro,
and Zacatecas (Fig.:).
~ithologic
and geochemical data, age
and tectonic setting of the different portions of s·..:..-=~~ i
t~e
GT are
=ed in tables 2 and 3.
7he Teloloapan subterrane is composed of calc-alkalic basalt, andesite and scarce rhyolite (Talavera, et al., 1993) interbedded with graywake, shale and limestone (Flg.31. This
assembla9~
has been metamorphosed to zeolite
to greenschist facies and is strongly deformed (Table 2) . The reefal limestones are Aptian-Albian in age and the volcanlclastic sequence is Hauterivian-Aptian in age based on the fossil fauna (Talavera, 1993).
---------------------
-
(ffi]
CENOZOIC VOLCANIC ROCKS (::::::::::§:, GUERRERO TERRANE
[gJ
JUAREZ TERRANE
I SME I SIERRA MADRE ORIENTAL I PRL I PARRAL TERRANE
cru VIZCAINO TERRANE
[ COA I COAHUILA TERRANE ~ MAYA TERRANE
[]QJ
XOLAPA TERRANE
rnKJ
MIXTECO TERRANE
[QK] OAXACA TERRANE []!!) CORTES TERRANE I CAS I CASORCA TEPRANE INAMI NORTH AMERICA CRATON SOOkm
~
LAPAZ
~.
Figure 1. Tectonostratigraphic terranes of Mexico (Coney and Campa, 1987).
tv tv
23
LASOlLAS CAMAlOTITO
300km
Figure 2
al.,
Guerrero subterranes of central Mexico (Campa et
1981)
Arcelia,
Guerrero
Telolopan,
subterranes:
Zihuatanejo,
Fresnillo-Zacatecas;
Huetamo,
Guanajuato,
and
Papanoa-Las Ollas-Camalotito. Guerrero basement: Arteaga and Placeres.
Table 2. Principal litholoqic anc chemical charact!~rist ics of s1J.bterra:1€s. SUBTERRANE TELOLOAPAN (1, 2)
SUBTERRANE ZIHUATANEJO (1, 2, 3)
SUBTERRANE HUETAMO
(1, 2)
LITHOLOGY
MAGMA':'IC SERIES
Volcaniclastic turbidites, reefal limestone, siliciclastic sedimentary rocks. AGE E Nd Hauterivian-Aptian +1.6+7.9 Aptian-Albian (Reefal limestone) LITHOLOGY Dacitic and rhyolitic ignimbrites, turbidites, reefal limestone. Shoshonitic basalt and andesite. AGE E Nd Albian+3.9 Turonian LITHOLOGY pillow basalt volcaniclastic rocks turbidites and reefal limestone .~GE
TithonianNeocomian; Aptian
Nd +6.5 to +7.9
E
ND
Guerrero
METAMORPHISM
C:llc-alkalinl~
"Sr/h'Sr
t~€
La/Lu 5.510.5
Zeolite to Greenshist facies SETTING Evolved island arc
MAGMATIC SERIES Calc-alkaline, tholeiitic, and shoshonitic
METAMORPHISM
4"iS r /S r
SETTING Evolved Island arc
!'('
0.70340.7052
La/Lu 9.7
MAGMATIC SERIES Tholeiitic, Calc-alkaline
Unmetamorphosed
METAMORPHISM Unmetamorphosed
'·'Sr87 /Sr~" L:l/Lu SETTING 0.7939 1-1.2 (Bas.) Back-arc basin 1.8-10.4 (Frags.)
tv
"'"
SUBTERRANE
l.ITHOLOGY
NE'l'AMI)F.PIII SM
MM-;MATIC
SEHIES
ARCELIA (1,
4, 5)
Bils:tlt. hyalocldsLites, dolpl-itic lu mi crogr1bbJ oie d~·kef. Klip('p;; of llltrdm1( il::: cllmulat.e. Radiolarian dwrt, hlack slwle. AGE
AlbianCen:>maniall SUB TERRANE LAS OLLAS (1,
4)
SUBTERRANE GUANAJUA'ro
(5 )
E Nd .'.1.5 to +8.0
LITHOLOGY
Thol"iil i·::: to tLkal i.:::
'Sr/Sr' llD
Pi llow basal t, pyr:>clastic rocks, diorite plagiogranite, gabro clinopyroxeni te AGE E Nd +7.1 to 114 -157 Ma (K-Ar) +9.1
La/Lu 0.6-4.4
MAGMATIC SERIES Tho:"eiitic
Exotic blockn of limestone, quartzite, chert, tuffs, pillow bas31t, anphibolite, gabbro, and ultra:nafic rocks. AGE E Nd Sr I Sr" Albian+8.1 to NC Cen:>manian +8.5 (K-Ar dates)
LITHOLOGY
PrehenitepumpelLyte
NETAMORPHISM Greenschits to amphib:>lite
(~a/Yb
0.7-0.9
MAGMATIC SERIES Tho2.eiitic
' 'Sr ISr"' 0.7035 0.7048
SETTING Back-arc basin
SETTING Melanges Subduction complex
t-tETAMORPHISM Greenschist
La/Lu ND
SETTING Oceanic arc (primitive)
IV Ul
Sl1BTERRANE ARPEROS (~ia,
5/), 6,
13)
SUB1'ERRANE SINALOA (7, 8, 9, 10)
SUBTERRANE FRESNILLO (11, 12)
Pelagic siliciclastic Alk~lic sedimentary rocks, limestone, basalt, radiolarite, doledte. AGE E::-Jd 'o
tv
43
estimated by the Consejo de Recursos Minerales (Henry, 1982). However, this figure includes epigenetic Tertiary deposits that occur in the same district. Pyrite, sphalerite, and chalcopyrite are present in all of the deposits (Table 5). Galena is present in most of
t~e
deposits but not in those located in Guanajuato and Baja California. Barite can be found in the deposits of the Teloloapan, Zihuatanejo, Arteaga, and Francisco I. Madero, Zacatecas, but not in the Papanoa-Las Ollas subterranes, or in the northern portion of the Guerrero terrane. Sulfosalts have been identified only in the Telolopan, Zihuatanejo, and Arteaga subterranes, with the exception of the Cedros Island deposit (Table 5). Cassiterite has been identified in La America and stannite in Tizapa. The only deposit with magnetite is La Minita. Pyrrotite is present in Campo Morado, Copper King, and Francisco I. Madero (Table 5).
Volcanogenic Deposits of the Teloloapan Subterrane The Rey de Plata, Campo Morado Group and Apaxtla VMS deposits are located in the Teloloapan subterrane (Fig. 10). The Teloloapan subterrane overrides the Sierra Madre Oriental along regional thrust faults at its eastern margin (Fig.l1), and is overlain by the Arcelia subterrane also on a thrust-fault contact (Campa and Ramirez, 1979, Talavera, 1993). Two
~ain
assemblages are present in the Teloloapan
subterrane. A basal volcanic unit 3500 m thick, and an
Table 4. Reserves and geochenlical character of the Guerrero terrane VMS and SEDEX deposits. Metric million Sn ppm Cu% Ref. tons Ag ppm Au ppm Pb % Zn% TELOLOAPAN SUBTERRANE 7.8 1 2.0 275 1.7 13 0.8 0.3 Rey de Plata R 3.1 37 2 6.0 112 1.2 1.1 0.7 Campo Morado R 2.3 2.3 750 3 0.01 226 2.8 0.1 Campo Seco GC 14.0 0.2 600 2.0 2.0 0.8 2 4 Aurora GC 0.1 14.0 518 2.3 2.3 0.5 5 Manto Rico GC 4.6 6.0 574 6 3.0 3.0 0.4 Suriana P 4.3 7.8 7 324 0.7 Tizapa R 1.9 1.9 0.3 279 1.4 1.4 3.5 0.1 8 Santa Rosa R ZIHUATANEJO Cuale E1 Bramador America E1 Rubi Amaltea La Minita
SUBTERRANE 2.0 R ? GC 0.1 R 0.5 R 0.5 R 6.0 R
ARTEAGA Arroyo Seco
R
165 212 310 250 90 58
1.1 1.2 1.0 0.3 0.5 0.0
1.1 3.1 1.0 0.3 0.5 0.3
4.7 12.0 7.5 12.0 7.4 4.5
0.3 0.6 0.2 1.5 0.4 0.2
2.0
180
0.0
2.8
0.5
0.0
PAPANOA-LAS OLLAS 2.0 Copper King GC
7
0.2
0.0
0.1
1.3
2
16
NORTH GUERRERO TERRANE 0.5 Guanajuato GC F. I. Madero GC 36.0 Calmalli 0.5 GC ? Cedros Island GC
3 31 26 20
0.2 0.0 4.8
0.0 0.9 0.1
0.0 1.7 2.5
16 17
26.4
4.4
46.6
0.2 0.0 2.9 0.8
17 18 19 17
R. - Reserves
P.- Production
2 9 77 4 0
9 10 11 12 13 14 15
2
GC.- Geochemical characterization
~ ~
45 Table 4 references:l.- Garcia et aJ., 1981; 2.- Lorenci and 1978; 3.- Mercado, 1993, oral personal communication; t.. - Heredia and Garcia, 1989; 5. - E~;pinosa, 1982, Montes, 1984; 6.- Pefioles, 1987 ; 7.- Minera Tizapa, 1993 unpublished data; 8.- Heredia and Garcia, 1988; 9.Solis and Macias, 1985; 10.- This work; 11.- Castafieda, 1983; 12.- Rosas, 1983; 13.- Berrocal et al., 1990; 14.Gayt~n et al. 1979; 15.-Librado, 1993; 16.- Y~fies, 1977; 17.- This work; 18.- Henry, 1982; 19.-Silva, 1983.
Mira~da,
Tahle 5. Minera logy of the
Guenel"O
py cp TELOLOAPAN SUBTERRANE Rey de Plata Campo Morado Campo Seeo Aurora Suriana Tizapa Santa Rosa
X X X X X X X
~p
X X X X X X X
X X X X X X X
tplrc1np gn
VMS
bet tt te fre pr bo cs st apy po el mt
X X X X X X
X
X X
X X X X
X
X
X X
X X X X
X X X X X
X X X X X
X
X
X
X X X
ARTEAGA Arroyo Seeo
X
X
X
X X X X
PAPANOA-LAS OLLAS Copper King
X
X
X
X
NORTH GUERRERO TERRANE Guanajuato X F. I. Madero X Calmalli X Cedros Island X
X X X
X X X X
py.tt.cs."· mt.-
X
X X
ZIHUATANEJO SUBTERRANE Cuale X El Bramador X America X El Rub! X Amaltea X La Minita X
X
and SEDEX deposits.
X X X X X
X
X
x
X
X
X X X X
X
X
X
X
X X
X
Pyrite; ep.- Chalcopyrite; sp.- Sphalerite; gn.- Galena; ba.- Barite; Tetrahedrite; te.- Tenantite; fre.- Freibergite; pr.- Pyrargirite; bo.- Bornite; Cassiterite; st.- Stannite; apy.- Arsenopyrite; po.- Pyrrotite; el.- Electrum; Magnetite. References: Same as Appendix A and this work.
.e=0'\
47 10'
~:?-
oC) a:
:>
Figure 19. Plan of the central portion of Rey de plata district (Penoles documents) . 0'\ V1
66
at Rey de Plata Mine at the northeast portion of the area. They were exploited during the early 1900's by open pit methods. Other lenses of similar dimensions are Escorpi6n, Manto I, Antares, Libra and Virgo lenses (Fig.13). Rey de Plata, Escorpi6n, and Antares bodies are stratigraphically located at the same horizon and are associated with black shale horizons. Virgo, Libra, and mantos I and Zn-Cu
are
stratigraphically higher (Fig.13).
Tehuixtla Body.- The Tehuixtla body is a lensoid
sulfide body 250 m long and reaches 25 m in its thickest portion (Figs.20 and 21). Smaller lenses are present below and above the main body (Fig.20). The Tehuixtla sulfide lens contains 1.1 Mt with 9.9 % Zn, 2.0 % Pb, 0.3 % Cu, 194 g/t Ag, and 0.7 g/t Au (Garcia-Fons, et al., 1981). The Tehuixtla body is hosted in a felsic metavolcanic unit that is located between two andesitic sequences (Fig.13). The rocks that underlie the Tehuixtla body are quartz-sericite schists strongly silicified in places, with abundant disseminated pyrite and barite veins. The groundmass of the schist is crypto to microcrystalline quartz with sericite around the aligned quartz crystals. These schist horizons are interbedded with matrix supported breccias containing angular fragments of quartz-sericite schist and black shale. The appearace of the breccias is turbiditic. The breccias have been replaced by barite, and
Figure 20. Tehuixtla body, cross-section A-A' (Modified Penoles documents).
~
...J
68
"0 OJ
• .-1
11-1 • .-1
"0 0
::E:
OJ I
OJ
t:
0
• .-1
oW
U
OJ
II)
I II) II)
0
~
u
>..
" 0
.0 f'C5 ...-l
oW
X
• .-1
='
..t: OJ
E-
'
4
C .0
~
A
0-
W
,....J "oJ
o
90
14 ~~\
100
¥
I 1\
110
115
,.~
•
rWlIlE
o
SI'III\I Fnll
o
TEIIUIXIIA BOOY
EO L1RnA BODY
Figure 29. Rey de Plata, Guerrero, 6"S histogram.
----------- -.
-
120
87
y-,.; 50
~ ~7-'1
o
40
• f'vnlTl:
en
o GALENII o SPlfIIlER,rE
.
rr: w
IW
2
6
30
,"
to. 6
----- ----
...,
0 ...
Figure 41_ Schematic tectono-stratigraphic column for the pre-Tertiary rocks of the Zacazonapan-Tejupilco area (Elias and Sanchez, 1992).
112
E
w
A A A A A A A A A A A AA A A A A A A A A A 0 0 °0 0 0 ° 0 _ 0 r"";;....,..::::..._.....;;.----_
- --......
~O
0
------_
1200m
ll00m
-
- - ___
00
00
--
0
00
...... -- -- -- --------- - - - - - -
~
~;...;:;;..:-
'
BASALT
CONGLOMERATE
r===l
t=::=.J
I I I':':, .', ',:, :j 0°
.....
B
GRAPHIT1C SCHIST
MASSIVE SULFIDES OISSEMINATEO SULFIDES
SERICITE SCHISTS
Figure 42. Schematic cross-section of Tizapa deposit (Ferioles data).
-
--
-
_ ... - - - - - - -
113
Table 6. Reserves of Tizapa deposit. TONS
BODY
Ag
Au
m
ppm
xlOOO
%
Zn
%
Cu
1411
10.7
2.2
313
1.7
8.8
0.6
M:
655
4.6
2.1
343
2.9
11.9
0.6
..v""
1778
8.0
1.4
311
1.7
5.6
0.9
.;~..,
,= .
3.4
2.7
375
1.4
7.9
0.4
..........
7.9
1.9
324
1.8
7.8
0.7
~
7:.7A:-
7~e
~$
;.~
~
le~s
cc~~ains
~!
:~?:
4!t
~J~:te
1.';1
she~~
!rc~
:~
~illio~
tab!e 6
~"'t-!:;rc~~:-.
be~~·t:e~ or~
r i~gs.
(Pe~oles.
41ter~ates
Ar.~ec!ll i~g
where pyrite is
::~~:t-te
tons. The reserve and grade u~published
datal.
411 the bodies W4S brecciated and later
c-::-:;::t-tt-:y cvergrown; pyrite !".-:-
%
ppm
L1
...-.-
~
Pb
with sphalerite in
between pyrite crystals is
c!lbu~d4nt.
Chalcopyrite is locc!lted
overgrown pyrlte crystals. Gc!llena and tetrahedrite
s~aree
a~d
fill
fr~cturQS
in pyrite. Sphc!llerite is
!ecd:sh In ecler c!lnd sometimes shows chc!llcopyrite disec!lse F:g.~8:.
Stanr.ite. arsenopyrite. pyrrhotite. boulc!lngerite
and !reiber;ite are rc!lfe c!lnd were identified by Macias '~;.~~bllshed ar~
scorc~
dc!lt4). Pyr!te framboids and colloform textures
(Mc!lcic!ls. unpubllshed data). A characteristic of
114 these lenses is that no underlying stringer zones nor jasperoid caps have been recognized.
La Esmeralda. Mexico.-
La Esmeralda is located
approximately 1 krn to the northeast of Tizapa mine (Fig.40). This deposit was explored by the Consejo de Recursos Minerales during the early 1980's. According to Rubinovich (1988), more than 20 buried lenses of more than 1 m in thickness were identified by drilling. The length of the lenses is not known but it is believed to be short. The reserves calculated by the Consejo de Recursos Minerales are 415,000 metric tons with 215 glt Ag, 2.2% Zn, and 1.2% Pb. Gold and Cu are below detection limits (Rubinovich, 1988). The sulfide-bearing lenses at La Esmeralda are not massive, and sulfidelgange is 20/80 (Rubinovich, 1988). The sulfide lenses are conformable with the host rock metamorphosed rhyolite tuff and chlorite and sericite schist. These units are stratigraphically higher than the Tizapa ore body. Rubinovich (1988) identified cassiterite, pyrite, arsenopyrite, galena, sphalerite, boulangerite, freibergite, owyheeite, chalcopyrite, bournonite, semseyite, berthierite, and jamesonite. Well-preserved pyrite framboids of different shapes survived metamorphism. Only a few pyrite overgrowths were recognized by Rubinovich (1988) in the pyrite of these deposits.
115 Volcanogenic Deposits of the Zihuatanejo Subterrane Cuale-El Bramador group, Jalisco.- This group includes the deposits El Rubi, Cuale, and El Desmoronado that have had past production. La America is presently being developed as a small producer. Figure 43 shows this group of VMS deposits, south of Puerto Vallarta, Jalisco. Rocks of the volcanosedimentary sequence that host the deposits are unmetamorphosed, but they have been intruded by Tertiary granitoid batholiths and covered by Tertiary felsic volcanic rocks.
Cvale, Jalisco.- The Cuale mining district was discovered
~n
1804. The company Union Cuale started operations at La Prieta Mine in that year and continued exploitation until 1854. Penoles company restarted operations in 1936 and closed in early 1940's. Fresnillo company began exploration in the area in 1972 and opened a metallurgical plant in 1980. Fresnillo company exploited several sulfide lenses from 1981 until 1992 at which time the Cuale ore-bodies were mined out. Two volcanosedimentary sequences are present in the Cuale district. The oldest sequence crops out in the southwestern portion of the district (Fig.45). The sequence comprises phyllite, and quartz-chlorite, quartz-biotite and quartz-sericite schist which are believed to represent metamorphosed felsic tuff. The age of this unit is unknown,
116
PACIFIC OCEAN
20°
25km
o
~
~
QUATERNARY TERTIARY VOLCANIC ROCKS
~ TERTIARY INTRUSIVE ROCKS
~
~ CRETACEOUS SEDIMENTARY AND VOLCANIC ROCKS ~
r-' ROAD
Figure 43. Cuale-El Bramador group, Jalisco.
-- ---------
----------
117
PERIOD
> a:
w Z w
• 8w a: w • .... ~
~
Cl.
. . .......· . - _........ .·......." ... ....... .. r, . . ,. " . . . . . . . . CUAl.E ....INC OISTTUCT. JALISCO
•
•
•
c
"
•
•
•
•
•
,.
•
•
•
•
•
c
•
~
•
•
"
•
•
"
•
•
•
•
•
'he
•
AHYCIDACITES. OUARTlLATnES. AtlYOlnES !EFFUSIVES AND FLOWS,
\101. CAtIOCl. AS TICS. \101. CANIC
BRECCIA. Willi flOWS
SHAlES. TurFACEOUS SIl lSlONES If.. "'10 SAItOS10NES. lun S "'lERAlIlAllOH .. LOWER PARl
CI)
::J
u
»
,.
•+
oW
•
,.
•
"
>
•t. •a: w a:
~
u
ieII' "CYOlnE PORPHYRY. GREENSlOtIE . .. CYOl lYE DOt.tE S
• • •
•
u in
CI)
•
a:
::J
-.
t
•
•
t
••• •
J'
PtfYlU1ES
• + •••
·.
\. • ieI' cnAHlT£S AHO ORAHOOfOAIJE S
Figure 44. Stratigraphic column of Cuale District (Berrocal
and Querol, 1991).
~'
RHYOLITE
,
I km
Figure 45. Composite stratigraphic section of Cuale district (Macias and Solis, 1985)
...... ...... 00
119 but is thought to be Triassic or lower Jurassic because of lithological similarity with the Arteaga schist (Macias and Solis, 1985). The upper sequence is upper Jurassic to lower Cretaceous in age as indicated by radiolaria and Raxhela found in siliciclastic sedimentary rocks (Ortigoza, 1983). The lower portion of the upper volcanic sequence is composed of porphyritic rhyolite. Shale, tuffaceous siltstone, and sandstone cover the porphyritic rhyolite. The youngest Cretaceous rocks are volcanic breccias and flows
(Berrocal
and Querol, 1991). This unit is intruded by granitoids 83 to 90 Ma and covered by Tertiary felsic volcanic rocks (Berrocal and Querol, 1991). The sulfide deposits are located on the upper portion of the porphyritic rhyolite and hosted in the shale and volcaniclastic sedimentary rocks that overlie the porphyritic flows and domes (Fig.46)
The more important
bodies are La Prieta, Chivos de Abajo, Chivos de Arriba, La Prietita, Jesus Maria, Patrocinio, Naricero, Socorredora, Coloradita y Minas del Oro. Detailed descriptions and petrography of the ore bodies may be found in Macias and Solis (1985) and Berrocal and Querol (1991). Grades and additional information on these bodies are listed in Appendix A. The Naricero body is, in fact, long, 195 m wide and 6.5 m
two tabular lenses 400 m
thick (Fig.47). It is hosted by
j
88COO
8/J00lLI_
t:
~~ (}(]O
+ + + + + + + + x )( x x x '+ + + + x x Tr x x x ~t",f>.,FAU~~ ~ - - ' J(~ + + + x )( )()( fI..~ )( )(' . + -+ + ~+ + x~ x x XQ~l X0
Ul
146 F~gure
63. El Rubi and Copper King textural variations.
A (RU-2). El Rubi. Parallel reflected light, F.o.v. 4 rnm. Coarse grained shattered pyrite in quartz matrix. From the underlying stockwork. B (RU-9). El Rubi. Parallel reflected light, F.o.v. 0.2 mm. Overgrown pyrite showing 120 C joints. Galena, chalcopyrite and sphalerite as the matrix. C (CK-8). Copper King. Parallel reflected light, F.o.v. 0.2 mm. Overgrown and partially annealed pyrite with pyrrhotite and chalcopyrite filling the spaces between pyrite. D (CK-8). Copper King. Reflected light, F.o.v. 0.2 mrn. Pyrite and sphalerite veinlets in pyrrhotite. Pyrite and pyrrhotite show reaction borders; sphalerite is the dark mineral in the center of the veinlet.
---
-------
147
148 lens suggest that the solutions were extracted from a raised stockworked vent zone and sulfides were deposited when solutions moved toward a lower pool.
Sulfur Isotopes. -
-4
0/00
up to +6
values are +22
range from
and center around zero. The barite
0/00
0/00.
The sulfide 6 34 S values
One pyrite analyzed by this writer is
+4.0 and two barites are +15.0 and +20.7 o/vo, in agreement with the values reported by Gonzalez-Partida, 1985 (Fig.64). These values are consistent with an igneous source of sulfur and the barite values with a Cretaceous seawater source.
El Desmoronado. Jalisco.- This district is located 20 km southwest of Talpa, Jalisco., in the same region as Cuale, La America and El Rubi
(Fig.43). The first known mining
extraction was in 1850 when the company Agraz-Basan processed 7 tons per day of high grade oxide Au-Ag ore. Mining continued until the early 1900's at which time ceased almost completely for the next 50 years. Zimapan, S.A. de C.V. company ~ith
mined 266,500 tons from Amaltea body
grades of 1 g/t Au, 154 gft Ag, 2.6% Pb, 13.6% Zn, and
1% eu (Berrocal, et al., 1990). The oldest rocks at El Desmoronado district are dacite and latite flows (Figs.65 and 66). They are overlain by felsic tuff that change laterally to black shale. Sulfide lenses rest on this paleosurface. Rhyolitic agglomerate and
-
--- - - - - - - - - - - - - - - - -
149
-15
-10
-5
o
+5
+10
+15
Figure 64. 6'''S histogram. El Rubi, Jalisco (Data from Gonzales-Partida, 1985).
...
- ---
-- .----
_..
--
----.-
-
150
000
o 0
0 ;....
0
0 0
°0 0
o
0
o
:
0
0 0
0
0
0
0 0
0
0
0
0 D
0
•
0
0 0
0
0 0
O.
_ _- _ - _ -
00
~ .. ~. . .~ ...
x
--
--
-
.
X
X
X
--
'.'
X
X
X
X X
X X >
~ J f,';~~;qGRANODIORITE ~ 'l "'-"-'.
a:
!
I
1°0°0° AGGLOMERATE
~ ~ a:
o
u
mLATITES
u
1:-.:::' ::::1 TUFFS
~
SULFIDE LENS WITH FEEDER ZONE
I J BLACK SHALES
DACITES
Figure 65. Composite stratigraphic section of El Desmoronado district, Jalisco .
.-
-----------------------
151
CCI'IRO LA BOLA
",
'.:'
.:'
.::..... . 200m
Figure 66. Structural section of El Desmoronadn district, Jdlisco. Rock units same as on figure 65.
152 time equivalent black shale rest on the tuff. The volcanic section is correlated to the Cretaceous volcanosedimentary sequence of the Guerrero terrane based on lithologic similarities. An early Tertiary age granodioritic pluton intrudes the Cretaceous rocks. Five sulfide lenses are present in the district (Fig.66). They are San Antonio-San Pedro, San Rafael
0
Cuatro Minas, Cinco Minas, and Cerro Bola-Amaltea. The lenses are from some tents of meters long and from 1 to 10 m thick, approximately. All of the lenses lie above dacite flows and underlie felsic tuff (Fig.65). The five sulfide lenses overlie a stockwork Z0nes of pyrite with a related silicified zone (Berrocal et al., 1990).
La Minita, Michoacan.- The La Minita deposit is located in the northwestern portion of Michoacan State. This deposit was discovered by Penoles company during the late 1970's (Gaytan, et al., 1979). Reserves prim to mining were 6 million tons with 48% barite, 4.0% Zn, 0.3% Pb, and 78 gft Ag. In the early 1990's the mine was in the process of closing due to exhausted reserves. The following description is taken from Ortigoza (1988) and Gaytan et al.
(1979).
The main deposit is Vulcano (Fig.67). This deposit is domal in shape and reaches a maximum thickness of 70 m. A stringer zone is present at the base of the deposit (Fig.68) .
153
§interbedd~d shaIe·limeslOne (U) WllJlldconic rocb(M} ~ massive li~stones(M)
r:::::I sl)ilitized woIconics
(1.)
-../'ithologic contoct -..,.... r~vet'se fauh _ normal foult :---1~o'ity t ___ -= In tel!!
o.
mentioned
3000
Figure 67. La Minita geological map (Penoles documents).
154
·Sci+SULF. 1
100 m
1 \A~.'fJ:-.A
,
I
\ \:17':.1/ \~~~I
A
Figure 68. Structural section of La Minita, Michoacar..
(Gaytan et al., 1979).
---
--
- - ----------------
155 Three rock units are defined in the area (Fig.69). The lower unit is porphyritic andesite, and basalt. The andesite is strongly propylitized. The middle unit hosts the Vulcano sulfide body and consists of rhyolitic ash-flow tuff, air-fall tuff, and lapilli tuff. It also contains volcaniclastic sedimentary rocks and reefal limestone. Some rhyolitic domes are present. This unit has been hydrothermally altered. Chlorite, quartz, barite veinlets, and secondary K-feldspar are the alteration minerals. Reefal limestone with caprinulid rudists are common. Ortigoza (1988) noted a gradation from fresh limestone to a quartz-magnetite zone and then to the Vulcano ore body. Tabular magnetite replacement bodies, reefal limestone, and
the orebody are hosted the same stratigraphic horizon.
They grade laterally into volcaniclastic sedimentary rocks acd tuffs. The upper unit consists of turbiditic strata interbedded with sandstone, and shale. It rests unconformably on the middle unit, and was apparently deposited in grabens (Gaytan, et al., 1979). The main sulfide deposits are Vulcano, Tabaquito, Sapo Negro, and Ojo de Agua. An irregular replacement body is present in the center portion, consists of hematite, magnetite, pyrite, and sphalerite (Ortigoza, 1988). Hematite replaces magnetite (Ortigoza, 1988). Jasper mixed with
156
..... Z ::::> a: w 0. 0.
::::>
--- -. -. -...... -. I
0 0
~
UMESTONE
I
I
I
~ V
V
v
'I ~
~
0
MAGNETITE BODIES
•
A
~
VOLCANICLASTIC ROCKS
4
A
Z ::::> a: w
SULFIDE AND SULFATE LENS
Y
y
. .....
SANDSTONE
I
..... 1
Z ::::> w -.J
SHALE
4
6
A
A
v
V
V V
V
V
-.J
V
v
V
V vJ
Figure 69. Composite stratigraphic section of La Minita, Michoacan. (Penoles documents) .
--
-----
----------------
157 brecciated limestone covers the body. A stockwork of chalcopyrite veinlets underlies the domal sulfide body at Vulcano. Two stratabound magnetite beds replace limestone
below the sulfide-sulfate body (Fig.69). Some
portions of the reefal limestone in contact with the ore body were replaced by magnetite. magnetite-quartz, and sulfide-sulfate veinlets are pervasive in the ore body. Some portions of the body are bedded. Two hematite-jasper beds are present at the southeastern portion of the pit (Ortigoza, 1988). El Tabaquito deposit
(Fig.67) is stratabound and is
stratigraphically in the same horizon as Vulcano. The deposit is made up of quartz and barite and contains sphalerite, galena and proustite. Jasperoid and stratabound manganiferus bodies located at Sapo Negro, approximately 3 km to the east of Vulcano, were interpreted by Ortigoza
(1988) as distal exhalite equivalents of the sulfate-sulfide o:::-e bodies. Sulfur isotope measurements from sulfides 15% to +14 6,4S, and from sulfates from +14
0/00
range from to +18
0/00
6:;s (Ortigoza, 1988). The sulfide values are centered around +2
0/00
(Fig.70). 6 34 S values might be interpreted as
sulfur derived from an igneous source that was later lightened. The barite values are similar to the Cretaceous seawater values (Claypool et al., 1980).
158
-10
-5
0
+5
+10
+15
Cl G 13
• 121
+20 PYRITE SPHALERITE CHALCOPYRITE BARITE GALENA
Figure 70. &'4S histogram for La Minita, Michoacan. (Data from Ortigoza, 1988).
159 Las Ollas Complex Copper King, Guerrero.- This deposit is located in The Las Ollas subterrane, at the southwestern coast of Guerrero State. A sequence of andesitic tuff, black slate, basaltic tuff and flows host two main sulfide lenses. The mafic sequence is intruded by a gabbro sill and a leucomonzonite (de Cserna et al., 1978). The thickness of the basaltic lavas and tuffs is approximately 200 m and that of the ur.cerlying andesitic tuffs is 150 m (Fig.71). The gabbro sill is 4 m thick and intrudes both sequences at their contact. These rocks have suffered metamorphism of lower greenschist facies
(de Cserna et al., 1978). Metamorphic
minerals in the mafic sequence are epidote, tremolite, and sphene. A Rb-Sr isochron determined from gabbro and leucomonzonite samples yielded an age of 311±30 Ma (de Cserna, et al., 1978). Several sulfide lenses are hosted in the lower portion of the basaltic sequence, close to the contact with the andesitic tuff. The Copper King lens is the largest in the region, but other smaller lenses are located at the EI Cinco area to the southeast (Fig.71). Copper King is approximately 150 m long and 50 m thick in the middle of the body. There is an stockwork of chalcopyrite, pyrite, quartz, chlorite, and calcite veinlets
at the base of this lens (Yanes, 1977)
and the lens is zoned. Sphalerite is more
160
~
S~TONE
CEJ r--r:r
lEUCOMONZONI rE L!L.J
~GABBRO
BASALTIC FlOWS AND TUFFS
,
[EJ
ANDESITIC TUFF
Pm
0_ _ _ _ _ _ _1.;.00 m
A
A'
200m
~~----~~------~--~--~~SEAl~EL
Figure 71. Copper King. Geological map (de Cserna et al., 1978) .
161 abundant in the upper part, while chalcopyrite and pyrrotite are more abundant at the bottom (Yanes, 1977). Pyrite comprises 60.5%, quartz 30%, pyrrhotite 5%, and chalcopyrite plus sphalerite 2.5% (Yanes, 1977). Fine grained silica is present laterally at the same stratigraphic level as the sulfide lens, suggesting that is a distal exhalite. The rock hosting the Copper King sulfide lens has been strongly silicified and contains chlorite vein1ets. Epidote, sphene, tremolite, and actinolite are common. The protholith of this rock is interpreted as andesite. ~rite
is euhedral suggesting that it has been
completely recrystallized. Chalcopyrite and pyrrhotite are located between pyrite crystals. Abundant pyrite veinlets with irregular borders replace pyrrhotite; suggesting that pyrrhotite may have been transformed to pyrite by fluids that also carried Zn and probably Cu, because sphalerite and chalcopyrite are banded in these veinlets (Fig.63 D). Chalcopyrite and pyrrhotite were also plastically deformed and remobilized after or during pyrite recrystallization as they fill spaces between euhedral pyrite (Fig.63). Lead and Ba are enriched at the upper portion of the Copper King body and coincide with a zone of high silica content. Higher concentrations of Zn, Cu, Au, and Ag are present at the middle portion of the sulfide body, where pyrrhotite, chlorite, and quartz are sparse and chalcopyrite is abundant (Fig.72). Chlorite and silica predominate above
162
en
a::
~ 10
1\
~
PO
o
CHLOR
a
Cpy
o
03
Zn~.
a
•
Cu~o
, 30' ,., ,;.: Ag ppm Au ppm Ba pc~
Figure 72. Copper King stratigraphic section and chemical profiles.
---
-- ---
---------------
163 and below the sulfide lens.
Sulfur Isotopes.- The
63~S
values from sulfides are shown in
figures 73 and 74. They range from -2.0 They are centered around 0
0100.
0/00
0/00
up to +3.0
(Figs.73 and 74). The
6'"S values of Copper King lens are from +1.7 to ~3.0 and the values below and above the lens are slightly negative. A possible interpretation of these values is that the S source may be igneous, with values very similar to the mantle value.
Arteaga Complex Arroyo Seeo, Miehoaean.- Arroyo Seco is located in the
southwestern portion of Michoacan State, 12 km to the northwest of Aguililla town. The oldest rock in the area is the Triassic Arteaga schist. This unit is unconformably covered by several kilometers of Cretaceous siliciclastic sedimentary rocks, reefal limestone, conglomerate, and rhyolitic to basaltic flows
and tuffs. Galena, pyrite, and small quantities of chalcopyrite
and sphalerite are hosted in carbonaceous shale of the Tepalcatepec Formation. This formation has been divided into three members (Fig.7S) in Arroyo Seco (Librado, 1992). The lower unit is sandstone interbedded with carbonaceous shale, and andesitic tuff, and coal seams.
164
-3
0
l8J
PYRRHOTITE
~
CHALCOPYRITE
+3
DELTA 34S
Figure 73. Copper King 6'IS histogram .
_------_._-.
.
--
165
• PYRRHOTITE • CHALCOPYRITE
en a: w 10
tu
~
\\ o~
-3
o
+3
DELTA 34 S Figure 74. vertical variation in 6 H s. Copper King, Guerrero.
-------------
--
166
UPPER CRETACEOUS RED CONGLOMERATES INTERBEDDED WITH SANDSTONES AND SHALES
TURONIAN·MAESTRICHTIAN LAVIEJA FORMATION
RHYOLITIC, ANDESITIC, AND BASALTIC FLOWS
REEFAL LIMESTONES
I~
MIDDLE CRETACEOUS CENOMANIAN·ALBIAN
ANDESmC TUFFS
TEPALCATEPEC F SANDSTONES INTERBEDDED WITH ANDESITIC TUFFS AND CARBONACEOUS SHALES WITH SULFIDES
LOWER CRETACEOUS BARRENIAN.APTIAN
.=::~.
TUFFS, BRECCIAS, AND BASALTIC AND ANDESmC FLOWS
TRIASSIC ARTEAGA SCHIST
Figure 75. Arroyo Seco stratigraphic column (Librado, 1992) .
...
_._.- -----------_.--_.
_.
167 Sulfides are hosted in this unit. The middle unit ranges from andesitic tuffs at the base to reefal limestone at the top (Fig.7S). Rhyolitic, andesitic, and basaltic flows overlie the middle unit. Mineralization is located in two areas at Arroyo Seco. Mineralization in the southern EI Zapote area consists of barite, galena, and sphalerite veins hosted in epidotized and chloritized andesitic tuffs and siltstone. Pyrite and chalcopyrite are rare. Sphalerite shows chalcopyrite disease textures. Barite is most abundant in this area. Galena and pyrite are hosted in carbonaceous shale and to lesser degree, in sandstone at Los Alacranes is located to the north. Sulfides are banded and stratified. Three mineralized horizons are each less than 10 m thick; the lower one is the longest, (2500 m), and thickest (10 m). Tetrahedrite and tennantite are included as very small grains in galena. Glauconite, ankerite, dolomite, and jasper are present in the upper portion of the mineralized sequence (Bustamante, et al., 1987; Bustamante and Esponda, 1991) . Galena is always associated with graphitic debris or with hydrocarbons in Los Alacranes area (Fig.77). The host rock is siltstone containing abundant plant debris with preserved cellular structures, locally partially replaced by calcite. Quartz and calcite commonly surround galena crystals. Barite occurs as veinlets and was later
------
-----
168
Ag76g/t Pb6'lC.
tOOOm 990m
SOm
I
~ Sandstone Interbedded wilh shales
Drilhole
~ S;tndstones Interbedded with black shales with disseminated sulfides ~ Graywackes Interbedded with 'uffs
~ Andesitic and basaniC IIows
Fig1Jre 76. Cross-section N7S"E, looking to the northwest, Arroyo Seeo, Michoacan (Librado, 1992).
-------------,.
-.
169 Figure 77. Arroyo Seco (AS), Michoacan, and San Ignacio (SI), and La Virgen (LV) or Arroyo de Cata, Guanajuato, textural variations. A (AS-I). Transmitted and reflected parallel light, F.o.v. 1 mm. Organic matter (black) and galena
(white)
veinlets in siltstone. B (AS-2). Transmitted and reflected light, F.o.v. 0.2 mm. Galena parallel to bedding in a coal bed. C (SI-7). Parallel reflected light, F.o.v. 0.2 mm. Fractured pyrite with chalcopyrite between fragments. D (LV-I). Transmitted and reflected polarized light, F.o.v. 2 mm. Fractured pyrite showing pull-apart fractures filled with fibrous quartz.
-------~~
-~
.--~~-.--------------
170
171 replaced by quartz and calcite, in the same way as was galena. Hydrocarbon veinlets contain galena surrounded by organic matter. Barite is also present in the same vein1ets and also replaces the host rock as large euhedral crystals. Rare pyrite is associated with calcite and replaces the borders of galena crystals.
Sulfur ISQtQpes.- Sulfides are high in light S, from -4.5 to -10.5 from +8.5 to +8.9
0/00 6~'s. 0/00
6~~s.
Sulfates contain heavier S, Sulfates from other deposits of
Guerrero Terrane contain S with higher values, generally from +15 to +20
0/00
6~~s
(Fig.78).
Discussion.- The environment of deposition of Arroyo Seco was a swamp close to a coast, where plants debris were deposited and preserved. The basin was developed in the Arteaga schist, and not directly in oceanic crust as elsewere other portions of the Guerrero terrane. Volcanism was active in the region and hydrothermal activity developed in the southern portion of the area. The rock textures observed at the northern portion are banded but were not necessarily formed by direct precipitation of sulfides under the sea. The abundance of galena in hydrocarbon veinlets suggest that Pb mineralization could have been produced, or at least remobilized after burial, as the product of basin metalliferous-hydrocarbons solutions. The S isotopes may be
172
·10
·5
I2J
GAlENA
•
BARITE
o OElTA34S
Figure 78. r,qS histogram. Arroyo Seco, Michoacan.
173 interpreted as reduced close to zero
63~S
that originally have values
for sulfides and to 15
0/00
0/00
for sulfates.
These are common values for VMS deposits of similar age deposited in the Guerrero terrane. The sulfide and sulfate reduction could happen after original deposition with a source located at the southern part of the system. This deposit has characteristics similar to SEDEX type of deposits rather than VMS. These characteristics are the association with clastic sedimentary rocks rather than with volcanic rocks, a basin with continental basement, at least in part, associated with basinal solutions rather than hydrothermal solutions from submarine vents. The high Pb content is in contrast with the
Z~-Pb-Cu
character of other
deposits of the same tectonostratigraphic terrane.
Northern Guerrero Terrane Francisco I. Madero, Zacatecas.- The Francisco I. Madero deposit is located in central Mexico, approximately 15 km northwest of Zacatecas City. The Consejo de Recursos Minerales Mexican government agency drilled 36, 000 m and sank a 126 m depth shaft, the San Francisco shaft, and developed two levels at 70 and 120 m depth. All workings are presently inaccessible. Henry (1982) interpreted the mineralization as replacement mantas related to a small granodiorite dike. The reserves calculated by the same author are 17-36
174 million tons with 2.0-3.5% Zn and 31-46 g/t Ag. Two portions modelled as minable by open-pit methods contain: Tepozan Open Pit.- 5.3 million tons with 3.8% Zn, 49 g/t Ag, 0.5% Pb, 0.2% Cu. Botecito Open Pit.- 2.2 million tons with 4.3% Zn, 39 g/t Ag, 0.8% pb, and 0.3% Cu. Three main sedimentary units are present. A lower unit
is composed of sericite-chlorite schist. The middle unit of calc-silicate horizons interbedded with abundant organic carbon and clays. A upper unit contains a higher proportion of calcium silicates and they increase upwards. The lower part of the lower unit hosts the lower manto. This portion contains black slates with abundant graphite and sedimentary recrystallized pyrite. This manto is the largest in the area and contains approximately 90% of the reserves. The thickness of this unit is approximately 200 m (Herrera-Mendieta, 1984). The graphitic layers are bedded within a groundmass of epidote, sphene, actinolite, diopside, and hedenbergite. The lower manto contains pyrrhotite, in massive bodies up to several meters thick with galena, chalcopyrite, galena-bismuthinite, and native bismuth. This lens has been interpreted as part of a skarn associated with Tertiary intrusions. Numerous minerals like matildite, hessite, aikinite, emplectite, wittichenite, and tsumoite were identified by Yta (1992, 1993). The middle unit contains pyrite laminations and minor
- --
----------------
175 chalcopyrite interbedded with black shale and red chert. Two mantos are hosted in this sequence (Fig.79): The ·lower tactite manto· and the ·upper tactite manto·
(Henry, 1982).
The upper part of the upper tactite manto is composed of quartz laminations interbedded with hematite. The general structure of Francisco I. Madero area is an anticline approximately N300W in trend. Several normal faults parallel to the anticline axis cut the mantas and displace them several tent of meters. One of these faults is known as the western fault.
Stratabound Mineralization.-The upper and middle portions of the metasedimentary sequence contain banded sulfide beds (Gomez-Caballero, oral personal communication). Pyrite is generally fractured and shows recrystallization. However, some porous and rounded framboids remnants are present in the central portion of euhedral, overgrown pyrite. Colloform pyrite is also present, but rare. Pull-apart fractures are cornmon. Pyrite is generally banded and parallel to beds of graphite, sericite, quartz, actinolite, and chlorite. Chalcopyrite, sphalerite, and galena are usually found as fillings between pyrite crystals and also banded and parallel to graphite lamellae (Fig.SO).
Correlation.- The black shale covered by limestone that host the bedded sulfide in Francisco I. Madero are lithologically
176
CARBONACeOUS IMETAMOnPHISEO lIMESTONE NTERBEDOeO WItH BI.-'CJ( SlATE
l.AMNA TED CHERT AKJ HEMA nrc "UPPER tACme-
t.UaIA TED ~ SI.A TES IWO BANDED PYRtE
"lOWER TAClITE MAN llE"
"lOWEnMANne-
,....,. ~ ,.., SERICITE.CHLORITE SCttlST
"""'"
Figure 79. Francisco I_ Madero stratigraphic column (Modified after Henry, 1982, and Herrera, 1984).
- - - - - - .-..
177
Figure 80. Francisco I. Madero textural variations. A (FIM-2). Transmitted parallel light, F.o.v. 4 mm. Lamellae of hematite and quartz. Arroyo El Molinito, Francisco I. Madero, Zacatecas. B (FIM-17). Laminated black shale interbedded with banded
pyrite.
C (FIM-20). Transmitted and reflected parallel light, F.o.v. 0.5 mm. Graphite (black)
, actinolite, chlorite,
calcite and quartz bands. Chalcopyrite (cp) is also banded and hosted in graphite. D (FIM-20B). Reflected parallel light, F.o.v. 0.5 mm. Shattered pyrite that has been partially overgrown and annealed.
178
-------------
--
179 similar to the black shale with Triassic lamellibranchs of the Zacatecas Formation described by Burckhardt (1905 and 1930). Both units underlie basaltic pillow lavas and dikes described in Zacatecas City, Fresnillo, and Francisco I. Madero. The black shale with bedded sulfide of Francisco I. Madero can be correlated with the Triassic siliciclastic sediments of Zacatecas City and Fresnillo.
Sulfur Isotopes.- The 6";$ of pyrite, galena, sphalerite, and pyrrhotite range between -0.6 to +1.9
0/00
and are
centered around zero (Fig.a1). These data rray be interpreted to show that the S source was igneous.
Guanajuato Group.-
Three occurrences of stratiform sulfide
bodies are present close to Guanajuato City (Fig.82). San Ignacio, Yolanda, and Arroyo de Catas are small lenses containing pyrite and small quantities of chalcopyrite and sphalerite that have been mined. They are hosted in the black slates interbedded with propylitized andesitic and basaltic flows and rhyolitic plugs (Fig. 83, Macias et al., 1991). The igneous rocks are 114-157 Ma dated by K-Ar with epsilon Nd +7.1 to +9.1 values indicating an oceanic affinity (Ortiz, et al., 1991).
San Ignacio.- The largest sulfide lens of this group is San Ignacio. It attains a thickness of up to 7 m in and is
180
i
-5
JTI 0
0
PYRITE
IZI
GALENA
[J
SPHALERITE
~
PYRRHOTITE
i
+5
DELTA34S
Figure 81. 6 14 S histogram. Francisco I. Madero, Zacatecas.
181
r
/'""'--..
,J
'-..../. . . }tYOLANDA '\
CERRO El GUAPlllO ' •
LA CONCEPCION
"'" \
\
• POlO
+
\
2105·
\
"\
~SAN IGNACIO
lOS MEXICANOS lkrn
Figurp 82. Guanajuato group.
182 101 14' 30"
101 13' 45·
2103'30"
2103'
A
A'
LOS MEXICANOS CREEK ARROYO DE CA TA LENS
J
SAN IGNACIO MINE
:::: ~~~~:~~~:::~::~:::::::~::::~~~§~:::::~::::~:~:~ff@ >
~
II:
~
l;;::J ....
VOLCANIC ROCKS
GRAYWACKE
If)
::l
1i11iSill ~':: u
,"" ~ ',," RHYOLITE, SLATE. SULFIDE LENS
5 t;;;~
PROPYLlTlZED VOLCANIC ROCKS
200m
Figure 83. San Ignacio and Arroyo de Cata or La Virgen area geologic map (Macias et al., 1991).
183 several tens of meters long (Fig.83 and 84). This lens is hosted in black slate that are overthrust by graywacke (Macias et ai., 1991)
(Fig.83).
A rhyolite body is located 300 m to the southwest of San Ignacio (Fig.83). The rhyolite porphyry is strongly argillized. It is spatially related to the sulfide lens. The rhyolite matrix is a foliated cryptocrystalline mass of quartz and sericite. S-C structures are common. The quartz phenocry'sts show undulating extinction. Some sodic plagioclase relicts have been preserved. The underlying slate have been silicified at several intensities. The slate have been replaced by cryptocrystalline quartz. Abundant quartz veinlets with rare chalcopyrite and pyrite show ductile deformation. Pyrite has been fractured. Fibrous quartz, parallel to the main stress direction, fills fractures in pyrite. Sphalerite is very rare and occurs with pyrite in fractures. Partial pyrite overgrowths are apparent. The sulfide lens is mainly composed of pyrite. Pyrite has been strongly fractured. Fibrous quartz is common between the fractured pyrite. Chalcopyrite is associated with the quartz filling. Rare sphalerite is included in pyrite. Pyrite was overgrown after fracturing. In some cases, pyrite was annealed and shows curved contacts that may be interpreted as pressure-solution borders (McClay, 1991). Macias et ai.
(1991) identified very rare pyrrhotite,
184
Figure 84. San ignacio cross-section (Randall et al., 1984).
185
and stannite inclusions in chalcopyrite.
Yclanda.- This sulfide lens is hosted in black slate and overlies a strongly argillized and silicified white probably rhyolitic flow. A strongly chloritized and epidotized green rock, probably andesite or basalt, is present in the same area, but its stratigraphic relationship is not clear because of the lack of outcrops. The underlying host rock is a quartz-sericite schist w~th
quartz phenocrysts and euhedral pyrite. Fibrous quartz
is present between the euhedral pyrite. Fractured pyrite is common. Sphalerite is very rare and is associated with the quartz matrix. Rare chalcopyrite, sphalerite, and bornite are also found as inclusions in pyrite. The pyrite texture is here interpreted as the product of fracturing and later overgrowing. The sulfide lens is mainly composed of overgrown pyrite. Rare frarnboidal pyrite is sometimes found in the center of euhedral to subhedral pyrite. Sparse chalcopyrite and sphalerite are located between the pyrite crystals and as inclusions.
Arroyo de Cata {La Virgen or EI Muertol .- This occurrence is located approximately 500 m southeast of San Ignacio (Fig.82). Pyrite is interbedded with black slate. The thickness of these strata is approximately 1 m. Pyrite has
186 been fractured and it is possible to put back together the fractured and sometimes rotated pieces. Chalcopyrite and sphalerite are very rare and fill some fractures in pyrite. Fibrous quartz fills the spaces between the pyrite fragments, parallel to the stretching direction. Annealing occurred after fracturing but it was not complete. Stress was concentrated in bands of sericite that was strongly deformed. Some overgrown and partially annealed pyrite was fractured again.
Sulfur Isotopes.- The
~"~S
values of sulfides of San Ignacio
and Yolanda are very similar (Fig.8S), between +2.7 and +6.2 0/00
for the former and from +2.9 to +3.7 0/00 for the
later. La Virgen values are negative, -3.1 to -3.4 0/00. The S source of these deposits seems different. San Ignacio and Yolanda are located close to rhyolitic bodies, while Arroyo de cata or La Virgen is far from the rhyolites. A possible interpretation of the S source is that the S from San Ignacio and Yolanda could come from an igneous source, while S from La Virgen could have been reduced by bacteria, related to a reducing environment where black shales were deposited.
Baja California Portion of Guerrero Terrane Three Cretaceous stratabound mineralized occurrences are known in Baja California. Calmalli and Cedros Island are
187
SAN IGNACIO
LA VIRGEN
YOLANDA
-15 -10 -5
Figure 85.
aJ4 S
o
+5 +10 +15 +20
histogram. San Ignacio, La Virgen or Arroyo
de Cata, and Yolanda, Guanajuato.
- ------
---
-----------
---
---
188 sulfide deposits related to mafic rocks (Fig.8). La Prosperidad is a banded Mn-Fe oxide deposit that overlies rhyolitic ash-flow tuffs (Jacobson, 1982).
Ca~ll!,
Baja California.- The Calma11i deposit is located
approximately 5 km north of E1 Arco porphyry copper deposit (Fig.8). Olivine and pyroxene peridotite and gabbro underlie pillow basalt interbedded with shale and chert in the area (Echavarri and Rangin, 1978). The stratabound sulfide body was identified by Echavarri and Rangin (1978). The underground workings are inaccessible at the present time. The mineralized body is hosted in basaltic flows and thin shales that have suffered greenschist metamorphism (Fig.86). The sulfide body has been oxidized. It is 40 m long, 25 m wide, and 2 m thick (Romero, 1988). The Jasper body contains fine grained silica, and hematite. Gold is enriched in this portion. The oxidized sulfide body is 140 m long, 60 m wide ,and up to 3 rn thick. It mainly contains hematite, goethite, malachite, and chrysocolla. Relict sulfides are present at the deeper portions of the mine. There, pyrite, sphalerite and chalcopyrite, and bornite were preserved (Romero, 1988). Table 7 shows the grades of the different parts of Calmalli deposit.
189
360m
340m
EZca
CALMALU BODY
C§:]
BASALTS
CEJ
GREEN SCHISTS
CD
20m
SCHISTS
7iaure 86. Calmalli, Baja California cross-section.
-
-------------
190 Table 7. Grade and tonnage of Calmalli deposit. ZONE
Metric
Thick-
tons
ness.
Au g/t
Ag g/t
Cu %
Zn %
m Oxides
30637
1.5
2.9
9.8
2.3
Sulf.
11226
2.0
2.5
23.0
3.6
4.4
Jasper
6131
2.5
7.2
28.6
2.2
0.5
Total
47994
2.0
4.6
21. 99
2.7
1.7
191 MASSIVE SULFIDE GEOCHEMISTRY The base metal content of the VMS deposits of each 3ubterrane of GT are distinctive. The ternary plots Pb-Zn-Cu of figures 87 and 88 shows those differences. Other classification schemes using precious metals and metallic ratios are described in this chapter. The following figures are referred to the average grade of each deposit. The data quality and the values used in the graphics are shown in Table 4. The numbers identify the deposits as follows: 1.- Rey de Plata.
11.- El Rubi.
2.- Campo Morado.
12.- Amaltea.
3 . - Campo Seco.
13.- Tizapa.
4.- Aurora.
14.- Santa Rosa.
5.- Manto Rico.
15.- La Minita.
6.- Suriana.
16.- Arroyo Seco.
7.- Copper King.
17.- San Ignacio (Guanajuato) .
8.- Cuale.
18.- Francisco I. Madero.
9. - El Bramador.
19.- Calmalli (Baja California) .
10.- La America.
20.- Cedros Island.
The Ag versus Pb, Zn, and Cu diagrams (Figs.89, 90, and 91) show that the Teloloapan and Zihuatanejo deposits overlap in a large field in Ag and base metal contents. However, some of the Teloloapan subterrane deposits are enriched in Ag and Pb while the Zihuatanejo deposits contain in general more Zn. The deposits located in Baja California, Zacatecas, and Arteaga are Ag depleted
192
Cu
1 REY DE PLATA 2 CAMPO MORADO 3CAMPOSECO 4 AURORAA 5 MANTO RICOA 6SURIANA 7 COPPER KING 8CUALE 9 EL BRAMADOR 10 AMERICA 11 RUBI 12AMALTEA 13TIZAPA 14 SANTA ROSA 15 LAMINITA 16 ARROYO SECOA 17 GUANAJUATO 18 FCO.I. MADERO A 19 CALMALlJ 20 CEDROS ISLAND
• VMS A SEOEX
Zn.Pb-Cu TYPE
2 •
PbTYPE 16
3
~ h
~10
11
~
13. 4 8' 15 18 514A9--.1 10 •
Pb ~----------------------~~~~.~12
• .20
VMS AND SEDEX OF THE GUERRERO TERRANE
Zn
Figure 87. Ternary plot of VMS and SEDEX deposits of Guerrero terrane .
.....
-- -_ .. _------------
193
Cu
AATEAGA
Pb
•
Pb-ZnTYPE
L - -_ _ _ _ _---==:::I-..~:::....IW
~----I
Zn
Figure 88. Cu-Fb-Zn compositional field (Large, 1992) of Guerrero terrane VMS and SEDEX deposits.
Agppm ~i
•
4
6 •
5
500
TELOLOAPAN • ZIHUATANEJO A PAPANOA-LAS OLLAS * ARTEAGA • B.C., GTO., AND ZAC. ()
400
300
•1 i.1
200
100
12
1-/
Q 17
o
3
~/
"'" A9
-.... ;,. "" ______________ ______________
15 .19A
*~7
...... •
•
_
0 18
~
~
2
0 20 ________________
4
L-______~
6
Pb% Figure 89. Ag versus pb.
f-' lO ~
Agppm 600
i
.. _'"
500
••
TELOLOAPAN ZIHUATANEJO PAPANOA-LAS OLLAS ARTEAGA B.C., GTO., AND ZAC.
400
t:
•
(I
300
31
1
11
~
. I
.'9 } I 100 I-
18 7
\7A"
• /
/
1J..~;'~
0*190 o
12
20 I
I
I
I
10
20
30
40
Q
Zn% Figure 90. Ag versus Zn. ~
\0
U1
Agppm 600
I
••
4
•
500
5
400
. •• .1 10
300
~A4 ~
.
f
0
oI
18
o
,
I
13
3
100
TELOLOAPAN ZIHUATANEJO PAPANOA-LAS OLLAS ARTEAGA B.C., GTO., AND ZAC.
A
----
0
17
I 0.5
•
c)
J ",
.&
.. -
*
~
9
2/
\.&
A
}11
~2---....!I
15
•
./
19
-"'" .,."" 20
0
1I
~ 7
o --:-'--1.5
2
2.5
3
Cu% Figure 91. Ag versus Cu.
I-' \0
CTI
197 compared with Teloloapan and Zihuatanejo deposits. Figures 92, 93, and 94 are Au versus Pb, Zn, and Cu plots. They indicate that Teloloapan subterrane deposits are enriched in Au with respect to the Zihuatanejo deposits. The Cedros Island deposit contains the highest Au values, but this number comes only from one sample. Calmalli, B.C., also shows a high value. The deposits from other portions of GT are depleted in Au and contain less than one ppm. Figure 95 shows a Au versus Ag plot. Three groups are apparent. Teloloapan and Zihuatanejo deposits overlap in sorr.e degree but Teloloapan has higher Ag content while Zihuatanejo lower content. Gold values are similar but Zihuatanejo deposits have less quantities than Teloloapan. Baja California, Guanajuato, Zacatecas, and Las OllasPapanca are Ag depleted and Au enriched. The same three groups discriminated in the last diagrams are apparent in figures 96 and 97. Silver and Au versus Pb+Zn+Cu plots indicate that Teloloapan deposits are richer in Ag and Au than those of Zihuatanejo subterrane although they overlap somewhat. The Baja California, Guanajuato, and Zacatecas deposits are depleted in both base and precious metals compared with the others. Figure 98 indicates that Teloloapan and Zihuatanejo in general overlap, but Zihuatanejo has a slightly higher Ag/Au ratio than Teloloapan. Baja California, Guanajuato, Zacatecas, and Papanoa-Las Ollas have remarkably low Ag/Au ratios and low
198 total base metals content. Figures 99, 100, and 101 are plots of Pb, Zn, and Cu, versus Pb/Zn+Cu+Pb, Zn/Zn+Cu+Pb, and Cu/Zn+Cu+Pb respectively. These diagrams may be interpreted as the overall importance of each element in the composition of the present sulfide in the deposit. Figure 99 shows that Pb is more abundant in the Teloloapan deposits than in Zihuatanejo deposits. Arteaga deposit contains more proportion of lead than all of the GT deposits. Baja California, Guanajuato, Zacatecas, and Papanoa-Las Ollas deposits have a very low Pb/Zn+Cu+Pb ratios. On the other hand, Zihuatanejo deposits present a ~ig~er
Zn/Zn+Cu+Pb ratios than all of the other groups of
depcsits
(Fig.lOO). There is a clear distinction with the
Teloloapan deposits. The Baja California, Guanajuato, Zacatecas, Arteaga, and Papanoa-Las Ollas deposits present a low Zn/Zn+Cu+Pb ratios.
The Cu/Zn+Cu+Pb ratios of Baja
California, Guanajuato, and Zacatecas are higher than those of Teloloapan, Zihuatanejo and Arteaga (Fig.101). Figure 101 contains compositional ternary diagrams of VMS deposits of GT. Teloloapan, Zihuatanejo, and Baja California, Guanajuato and Zacatecas deposits can be discriminated
on the Sn-Au-Pb+Zn+Cu and Sn-Ag-Pb+Zn+Cu
diagrams. The stronger contrast is obtained in the Ag-Au-Pb+Zn+Cu diagram. Teloloapan and Zihuatanejo deposits overlap in one
199 part, but Teloloapan has less proportion of Pb+Zn+Cu than Zihuatanejo. Silver content is similar and Au is higher in Teloloapan (Fig.103).
Au ppm
o------------------~
20
25
TELOLOAPAN • ZIHUATANEJO • PAPANOA·LAS OLLAS * ARTEAGA· B.C., GTO., AND ZAC. 0
20
15
10
19
51 0 17 7 15
2 10 14 .13 18 _ .
1 0-*-4--0 o 1
8 Il1Al .11 2
3 •
1
.~I3
18
______
~----
6
•
5
~------~------J 4
• ____
4
5
6
7
Pb% Figure 92. Au versus pb. tv
o o
Au ppm 5
i
4
3 .-
2
o
19
TELOLOAPAN • ZIHUATANEJO A PAPANOA-LAS OLLAS * ARTEAGA • B.C., GTO., AND ZAC. 0
"r---------_____.
s
13.
14
Figure 93. Au versus Zn. I\J
o
I-'
Au ppm 20(--:)
25
TELOLOAPAN • ZIHUATANEJO A PAPANOA·LAS OLLAS * ARTEAGA • B.C., GTO., AND ZAC. 0
20
15
10 .-
190
5
• 17l 1~ .5 91 2•
3
10.8
14e: 1618 -
°FlI
•
13
I ...
0.5
4
3
I
1
*7
... 11 1:5
2
2.5
Cu % Figure 94. Au versus Cu. tv
o
tv
Au ppm 0
25 \--
20
15
20
TELOLOAPAN ZIHUATANEJO PAPANOA-LAS OLLAS ARTEAGA B.C., GTO., ZAC.
~
I
• A
*• 0
10
5
l-
19
0
6
400
500
600 tv
Figure 95. Au versus Ag.
o
1JJ
Agppm 600 •
4
6
•
TELOLOAPAN • ZIHUATANEJO A PAPANOA·LAS OLLAS * ARTEAGA· B.C., GTO, AND ZAC. 0
500
400 .-
300
11
A\
16
A9
200
/
1P", /
100
17
~\!" , / 12 19
o (I"\.J.,. 7
o
20
o
0
10
20
30
40
50
Pb+Zn+Cu% Figure 96. Ag versus Pb+Zn+Cu. tv
o
01::-
Au ppm 20
25
0
TELOLOAPAN· ZIHUATANEJO A PAPANOA-LAS OLLAS ARTEAGA. B.C., GTO., AND ZAC. 0
20
*
15
10
19
17
l
~'
3
5 I-
08
71"I/J...
0i('"CI.
1~_. 13 _1
-
_.. 9
•4 • 5
114 20
10
Pb+Zn+
~~-_
-' _ _ _ _ _
C
30
U
Of
40
50
10
Figure 97. Au versus Pb+Zn+Cu. tv
o
V1
Ag/Au ppm 800~
11
I
600 f-
400
"
I-
A
,
,
I
,
I
I
TELOLOAPAN • ZIHUATANEJO A PAPANOA-LAS OLLAS * ARTEAGA • B.C., GTO., ZAC. 0
I
200
20 OV17
o
I
'0
0
10
20
30
40
80
Zn+Cu+Pb% Figure 98. Ag/Au versus Zn+Cu+Pb. IV
o
0'1
Pb% 7
/5
i
_
6
4 5
20
•
(l
•
TELOLOAPAN • ZIHUATANEJO A PAPANOA·LAS OLLAS * ARTEAGA· B.C., GTO., ZAC. (I
6
4 ~
3
,,/J I I A
•
13
2 1
16
~
;7 I
1
10 /
A
& 12 1 ..
1
/S-!!2 ,
0*Q19~ " u
0.2
0.4
0.6
0.8
Pb/Zn+Cu+Pb % Figure 99. Pb versus Pb/Zn+Cu+Pb. tv
o
--.]
Zn%
,-)
20'~
40 1-
30
~
TELOLOAPAN • ZIHUATANEJO A PAPANOA-LAS OLLAS * ARTEAGA • B.C., GTO., ZAC. •
20
10
00 17 o
*7 __
~-a-~
____________~______________L -_ _ _ _ _ _ _ _ _ _ _ _~_ _ _ _~
0.2
0.4
0.6
0.8
Zn/Zn+Cu+Pb % Figure 100. Zn versus Zn/Zn+Cu+Pb. r-J
o
00
Cu%
.----------------------n------------·---------. 19
-
TELOLOAPAN e ZIHUATANEJO A PAPANOA-LAS OLLAS * ARTEAGA • B.C., GTO., AND ZAC. 0
2.5
2 11
A
1.5
*7 1
20 4
oee13
59. 0.5
I-e.
0.-
e
2
e6
2"8 A&1015 e314
o
17 -I _
0.2
0.4
0.6
0.8
o
_-'
1
Cu/Zn+Cu+Pb % Figure 101. Cu versus Cu/Zn+Cu+Pb. N
o
lO
Pb/Zn+Cu+Pb % .8
18
0.8
TELOLOAPAN • ZIHUATANEJO A PAPANOA-LAS OLLAS * ARTEAGAB.C., GTO., AND ZAC.
