GSN Regular Membership Meeting, Reno, Nevada

Description

Contact: gsn@gsnv.org

GSN MEETING in RENO—FRIDAY, MARCH 10, 2023

(NOTE ONE WEEK EARLIER THAN NORMAL!)

GUEST SPEAKER:  Richard Bedell

Title:  “Magmatism, Granitic Pegmatite Genesis and    Associated Mineralization”

Sponsor:  FALCON DRILLING INC.

TIME: Drinks @ 6 pm, Dinner @ 6:30 pm, Talk @ 7:30 pm

WHERE:  Hidden Valley Country Club, 3575 E. Hidden Valley Dr., Reno

 DINNER COST:  $50.00 (REGISTER OR RSVP BELOW ABSTRACT. Student Members eat free as long as you RSVP.)

(PLEASE RSVP BY FRIDAY, March 3, 2023 at 4 PM! I leave for PDAC on Mar. 4th.)

ABSTRACT:

Our understanding of magma reservoirs has changed considerably from convecting, melt dominated, to conductive, crystal rich magma chambers. Water rich I type granites usually related to subduction zones with high oxygen fugacities, that approach their liquidus partitioning S and Cl, can create porphyry deposits. Pegmatites, on the other hand, are produced from A and S type granites and are generally broken down into LCT (Li, Ce, Ta) or NYF (Nb, Y, F) types.

Pegmatites are further defined by distance from source pluton and can be hosted within the roof zone , on the margins or increasingly distal. Generally, the more distal the more fractionated. This long held observation now can be genetically explained by the abundance of melt dominated H2O rich magmatic volatile phase (MVP) vs. abundance of crystal mush. Pegmatites are now thought to be generated within magma chambers with high crystallinity (>70-75%) whereby MVP is trapped within the crystalline mush and the pegmatites form from a pressurized solute-rich MVP (Troch et al. 2022).

Classic zoned pegmatites of greatest mineralogical interest, crystallize well below their solidus and invoke disequilibrium textures such as graphic granite, Unidirectional Solidification Texture (UST) and line rock. The shallowest pegmatites, approaching or in the epithermal zone can have open pockets allowing crystals to grow that are coveted by collectors. These pegmatites also may be zoned allowing further concentration of incompatible elements. These pegmatites that are LCT have the greatest chance of providing Li ore in spodumene concentrated usually in late cleavelandite (bladed albite) replacement zones.

The deeper pegmatites are emplaced into hotter host rocks that may be even suprasolidus. These can be generated through direct anatexis and are typically unzoned. They are emplaced more by replacement than dilation and therefore country rock can have a major effect on pegmatite bulk composition. An example is shown of the Madawaska Mine in Bancroft Ontario where U & Th grades are well correlated with the assimilation of iron rich metagabbro.

Lots of good igneous petrology and mineral photos.

The Canadian Mineralogist Vol. 60, pp. 229-248 (2022) DOI: 10.3749/canmin.1800006 A Proposed New Mineralogical Classification System For Granitic Pegmatites M. A. Wise , A. Muller, W.B. Simmons.

American Mineralogist, Volume 107, pages 190–205, 2022; The physical and chemical evolution of magmatic fluids in near-solidus silicic magma reservoirs: Implications for the formation of pegmatites. J. Troch, C. Huber , and O. Bachmann

Maine-pegmatite-workshop.com Sept. 7-10, 2023, Bethel ME.

 

Bio: Richard L. Bedell

Currently Chairman of the Board of TerraCore Inc. an international drill core imaging technology company, a Board member of the Geological Society of Nevada Foundation and Technical Advisor to Westward Gold and Gold Bull Resources. Also, on a JPL working group for algorithm development on the next generation of Earth observing satellites. Richard has almost 40 years international exploration experience including an adjunct Faculty position in Exploration Geophysics at The Mackay School of Earth Sciences and Engineering University Nevada Reno. Previously cofounder (with Ron Parratt) of AuEx Ventures that did the successful Exploration on the Long Canyon Deposit in Nevada. After AuEx was sold became cofounder (with Ron Parratt) of Renaissance Gold that merged with EVRIM Resources to create Orogen Royalties that have assets in Nevada, Mexico, and British Columbia. Previously also with Homestake Mining as part of their global target selection team and ran the technical group worldwide for exploration, as well as exploration for BP Minerals and Rio Tinto. He is a recognized expert in remote sensing and geo-spatial technologies and is a Fellow of the Society of Economic Geologists, a member of the Geological Society of America, founding member of the Geologic Remote Sensing Group, and a member and past President of the Geological Society of Nevada. Richard is a graduate from the school of Natural Sciences & Mathematics from Hampshire College in Massachusetts with a B.A., an M.Sc. at the University of Toronto in Economic Geology, and a second M.Sc. from the University of London in Remote Sensing and GIS.

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