Applied Structural Geology

Unravelling Structural History Through Alteration Mapping Anna Fonseca, Dr. Ivo Vos, Dr. Julia Kramer - SRK Consulting Canada Dr. Bert DeWaele, Mathieu Lacorde - SRK Consulting Australasia

Saskatchewan Open House December 2, 2014

Overview • Structural versus alteration mapping • Alteration mapping tools − Digital alteration mapping − Infrared spectroscopy  Types of data acquired from infrared spectroscopy  Fault controlled alteration assymetry • Case studies • Concluding Remarks


Structural vs. Alteration Mapping Alteration mapping

Structural mapping 220 structural measurements

Structural mapping: targeted at key fault/intersection exposures

23 structural measurements 220 chip samples and analyses

Alteration mapping: systematic, aiming at maximum coverage


Structural vs. Alteration Mapping Steeply plunging quartz growth fibres recording synmineralization normal sense of movement on the fault

Brittle fault characterization during an alteration mapping project: •

Document kinematic indicators

•

Search for indicators of the earliest or/and synmineralization movement

•

Document indicators of later movement on the fault

•

Compare the alteration on both sides of the fault

•

Investigate alteration assymetry

Subhorizontal slickenlines indicate dextral sense of movement on the same fault


Structural vs. Alteration Mapping Breccia characterization during an alteration mapping project: •

Polymict or monomict?

•

In situ (monomict) or mixed lithologies?

•

Cemented?

•

Rebrecciation?

•

Geometry? (diatreme should not be used as a default term)

Polymict

Sulphide cement

Re-brecciated


Monomict in situ

Alunite replaced clasts

Fault wedge

Structural vs. Alteration Mapping Required on traverse: Required on traverse:

Required in camp/hotel: Desirable on traverse: Project specific:


Digital Alteration Mapping Hardware • Large volume of data collected while traversing • Need to analyze, interpret, and plot updated maps daily

Software

• Need to plan/adjust the next day’s traverse accordingly GIS Pro App


Digital Alteration Mapping • Enter a large volume of information from statistical sampling along long traverses • Plot traverses and analytical results each evening • Make maps of each mineral zone (very important) • Optimize the next day’s traverse • Consult geochemical, geophysical, drilling, or other exploration information while mapping • Prevents the geologist from filtering or interpreting data while away from the outcrop • Consistency: “asks” for the same information every time


Infrared Spectroscopy Required Field Equipment – Infrared Spectrometers Without IRS it’s not possible to identify most alteration minerals

PIMA Specterra Terraspec

ArcOptix

Avantes Saskatchewan Open House December 2, 2014

Ocean Optics

Infrared Spectroscopy Field Approach – Chip Sampling • Outcrop (preferably) • Small samples • At least 1 surface >1 cm free of weathering rind (don’t write on that surface)

• Representative • Statistical sample suite

Without IRS it’s not possible to identify most alteration minerals Saskatchewan Open House December 2, 2014

Infrared Spectroscopy Three main types of information • Presence/absence of a mineral species • Chemical composition • Spectral feature extractions (quantitative and semi-quantitative data)

Alunite is present


Infrared Spectroscopy Three main types of information • Presence/absence of a mineral species • Chemical composition • Spectral feature extractions (quantitative and semi-quantitative data)

NH4-bearing illite


Infrared Spectroscopy Three main types of information

Kaolinite crystallinity index

2200 nm

1900 nm

2180 nm

2160 nm

• Presence/absence of a mineral species • Chemical composition • Spectral feature extractions (quantitative and semi-quantitative data)

Illite crystallinity index Saskatchewan Open House December 2, 2014

Concluding Remarks • The geologist mapping alteration cannot ignore structure. • The structural geologist has much to gain from alteration mapping. • Alteration provides important information about the structural history of a mineral property, particularly in seismically active areas with postmineralization fault reactivation. • Structure and alteration mapping is best done by a pair of specialists, but can be done by a single mapper. • Combined structural and alteration mapping provide higher quality exploration targets.
