8:30 AM - 5:00 PM

1 day course

ORGANIZER: Society of Economic Geologists (SEG)

LEVEL OF COMPREHENSION: Geologists involved in the exploration for epithermal Au and porphyry Cu deposits

Porphyry Cu (±Au) deposits account for ~70% of global Cu production. Increasingly, porphyry Cu deposits are explored for – and discovered – beneath cover, both syn-mineral lithocaps up to ~1 km thick, as well as post-mineral cover. Lithocaps form in the epithermal (<1 km deep) environment; permeable lithologic horizons are altered to residual quartz with halos of quartz-alunite and other advanced argillic minerals, and have structurally controlled feeder zones; they are coupled genetically to deeper potassic alteration of underlying porphyry deposits. Lithocaps are sterile in metals on formation, but some are subsequently mineralized with Au and Cu (as high sulfidation-state sulfides), related to ascent of post-potassic fluid that overprints the porphyry system.

This course will examine the formation of lithocaps, and discuss their characteristics and alteration zoning, and – in some cases – high-sulfidation mineralization; epithermal veins also form on the margins of lithocaps. The transition of lithocaps to the tops of underlying porphyry Cu±Au deposits will be examined, including controls on the mineralogical zonation. Numerous examples will be used, and features that assist with exploration and assessment will be stressed. This course is principally for geologists in exploration with experience working in the field.

TOP TAKEAWAYS:

• Porphyry Cu(Au) deposits form in volcanic arcs and are responsible for 70% of global Cu production, 50% of Mo, and significant Au, Ag Re, In, Ge, Pd, Te, Se, Bi, Zn, and Pb

• Porphyry deposits form beneath a lithocap horizon of alteration up to ~1 km thick, masking the deposit unless deeply eroded

• Lithocaps have alteration characteristics that provide guides to exploration for porphyry deposits

• Such guidelines include: lithocaps form on the shoulders of porphyry deposits, and pyrophyllite to white mica defines the transition to the tops of porphyry deposits

• Although barren on formation, some lithocaps may become mineralized with Au and Cu, the latter as high sulfidation-state sulfides, with highest grades located in feeder zones of the lithocap

LAPTOPS REQUIRED TO VIEW DIGITAL MANUAL

COURSE FEES: SOLD OUT

Includes course material, continental breakfast and lunch