GSN Regular Membership Meeting, Reno, NV

Description

Contact: gsn@gsnv.org

GSN REGULAR MEMBERSHIP—SEPTEMBER 15, 2023 MEETING

The GSN Regular Membership Meeting will be held at the Atlantis Hotel & Casino this year!

Guest Speaker:  Alexander Holmwood

Title:  “Temporal evolution of the Majuba Hill Cu-(Mo)-(Sn) deposit, Pershing County, Nevada”

Date:   Friday, September 15, 2023

Time:  Drinks @ 6:00 pm, Dinner @ 6:30 pm, Talk @ 7:30 pm

Location:  Atlantis Hotel and Casino

Dinner Cost: $60.00 per person

Reservations are due by 5 p.m. on MONDAY, SEPTEMBER 11th!

NOTE: You will be invoiced $60 if you do not cancel your reservation by Wednesday, September 13th.

Payment Options:

• SCROLL DOWN TO PREPAY FOR DINNER WITH A CREDIT CARD
  
• SCROLL DOWN TO RSVP and pay at the door
• Non-Members Social Hour cost is $10 payable at the door

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Abstract:

The Majuba Hill intrusive complex of northwestern Nevada exhibits two superimposed hydrothermal mineral deposits. Quartz vein-hosted Cu-(Mo) mineralization occurring in Jurassic (~160 Ma) granodiorite was later overprinted by Oligocene (~25 Ma) subvolcanic rhyolite magmatism and related Cu-(Mo)-(Sn) mineralization.

The Jurassic hydrothermal system is characterized by early barren to molybdenite-bearing granular quartz veins and barren comb-textured quartz veins reopened by later tourmaline, calcite, and chlorite. Fractures in early veins provided pathways for tourmaline, calcite, chlorite, and later sulfide deposition. Hydrothermal Cu occurs as anhedral chalcopyrite overprinting earlier veins and gangue minerals.

Oligocene hydrothermal deposition commenced with granular quartz + (molybdenite) veins and barren comb-textured quartz veins crosscutting subvolcanic rhyolites. Euhedral cassiterite + tourmaline + quartz mineralization (~25 Ma) followed and accompanied significant tourmaline + quartz + sericite + fluorite deposition and alteration of porphyritic rhyolites. Anhedral chalcopyrite deposited as disseminated crystals overprinting altered K-feldspar phenocrysts and by infilling portions of open space-filling veins. Chalcopyrite also crosscuts euhedral quartz-arsenopyrite veins. Subequal amounts of pyrrhotite and minor sphalerite are spatially associated with chalcopyrite but precipitated earlier.

Shallow portions of the Majuba Hill deposit were affected by a supergene fluid that deposited digenite + (covellite) along the margins of hypogene chalcopyrite crystals. Minor cuprite and native Cu were also observed in drill hole MHB9 but appear less common than digenite and covellite.

Paragenetic sequences from both the Jurassic and Oligocene hydrothermal systems suggest the sulfidation state of parent hydrothermal fluid(s) increased over the duration of each system. The genetic association between cassiterite, hydrothermal tourmaline + quartz, and emplacement of subvolcanic rhyolites suggests Sn endowment may be derived from a peraluminous and fractionated parent intrusion. These genetic associations are similar to those observed in Bolivian rhyolite-hosted Sn deposits. Significant hypogene and supergene hydrothermal Cu systems like those at Majuba Hill, however, are absent in the Bolivian deposits.

Bio:

Alex Holmwood grew up near Buffalo, New York and spent eight summers canoe tripping throughout Ontario and southern Québec. These many summers in remote parts of the Canadian Shield initiated his curiosity in natural sciences, and he decided to take an introductory geology course during his first semester at Hamilton College. He hasn’t looked back since, and he graduated with a B.A. in Geosciences from Hamilton in 2019. He also studied abroad in Nepal and Scotland while an undergraduate, and he completed a research internship through the Lunar and Planetary Instituted during the summer of 2018. Alex completed his M.Sc. in Geology from the University of Nevada, Reno in 2023, and has been working for Lahontan Gold on their Santa Fe Project since graduating.