Description

Location: Western Folklife Center, Elko, NV

Contact: justin.b.milliard@gmail.com

This month’s GSN Elko Chapter meeting will be held at the Western Folk Life Center on Thursday, January 20, 2022

After four months of hybrid talks with varying degrees of success in our virtual presentation component, with plenty of frustration by both our volunteer officers and virtual attendees voicing their displeasure with audio/visual quality we will be returning to 100% in person presentations in 2022. So please attend if you want to enjoy the presentation, soak up some knowledge, suds, and social merriment.

Thursday, January 20th

Food and drinks @ 6 pm and talk to begin at 7 pm.

Presenter: David R. Ernst, Exploration Manager for Kinross – Bald Mountain

Title: Bald Mountain District Geology, White Pine County, Nevada

 Abstract: 

The Bald Mountain District is located on the southeast extension of the Carlin Trend at the southern end of the Ruby Mountains in White Pine County, Nevada. The district has produced over 6 million ounces of gold and has a resource of nearly 6 million ounces of gold.  The property covers over 131,000 acres and is considered the largest contiguous land position in the United States. The first claims in the district were staked in 1869 in the northern portion of the district and modern exploration for gold has been conducted for over forty-five years. Outcropping ore-bodies were discovered long ago. Current efforts focus on prospective areas covered by post-mineral volcanics and/or alluvium, areas that were neglected due to low grade drill results, and areas where poor host rocks may hide deposits in permissive stratigraphic horizons. Where possible, structural intersections at permissive host rock horizons are targeted.

Two gold mineralizing events occurred at Bald Mountain: Jurassic-age intrusive-related and Eocene-age sediment-hosted. During the Middle Jurassic Period,  gold deposits formed on the margins of intrusive bodies. The Jurassic-aged Bald Mountain Stock and intrusive-related deposits occur along a broad structural zone trending northwest from the Bida deposit through Top to Redbird/Numbers. This structural zone is called the Bida Trend. Gold mineralization is concentrated on the NW and SE ends of the stock, especially at the intersection of the Bida Trend with a major structural corridor bounded by the Dynasty and West Top Faults. These deposits are hosted by several sedimentary units ranging in age from Cambrian to Mississippian. At Top, units that host the majority of the gold are the Cambrian Windfall and Ordovician Pogonip Formations, and Jurassic intrusives. The deposit dips moderately to the east to northeast and is open at depth. In general, intrusion-related deposits are deeply oxidized, and at Top, oxidation extends to over 2500 feet below the surface.

The second mineralizing event occurred in the Eocene. This younger event produced gold mineralization and deposits that are similar to the gold deposits at Carlin in that they are sediment-hosted and disseminated. Carlin type deposits occur in specific horizons at the top of the Devonian Guilmette Limestone, in the Mississippian Pilot Formation, or in Joana Limestone and the base of the Chainman Formation. The best host rocks are formations with silt/sand grains with carbonate (calcite or dolomite) cement. Where the intrusive-related deposits appear to be

overprinted by Carlin type deposits, we have hybrid deposits.  There are thick parts of the stratigraphic section that make poor hosts, specifically massive sections of limestone and dolomite. In some target areas, these sections of barren rock can hide gold-bearing zones below.

Deposits occur where rocks are strongly deformed along faults and fault intersections, especially in the permissive host rock horizons. Structural intersections at permissive host rock horizons are targets for exploration. The important structural trends that control mineralization in the district are: NNE, NW, NNW, and WSW. Low-angle structures, both compressional and extensional, and folds can also be important. The structural evolution in northern Nevada is complex. Several tectonic episodes have deformed and displaced the stratigraphic units in the region and many faults have been reactivated at various times as stress regimes have changed. Post-mineral deformation was extensional. This tectonism formed the Great Basin’s basin and range physiographic province that exists today and has affected the rocks and gold deposits at Bald Mountain. Some of the displacement appears to be lateral along strike-slip or oblique-slip faulting.

The two deposit types have different chemistry. Intrusive-related deposits have a trace element signature of Cu, Ag, Mo, Bi, Te (As and Sb) while the Carlin type systems have As, Sb, Hg, Tl. Intrusive-related deposits contain high grades locally and coarser gold while the Carlin systems have fine-grained gold that is more evenly disseminated. Oxidation and the refractory nature of carbon in the ores are different in the two deposit types. Carbon is not always refractory or preg robbing in the intrusive-related deposits while carbonaceous, sulfide bearing material in the Carlin type deposits is refractory. Copper can be an issue in intrusive-related deposits because it competes with gold in reaction to cyanide.

The size and grade of the two deposit types is a consideration because the intrusive-related deposits tend to be larger and higher grade. However, Vantage is a Carlin type deposit that averaged 4 gpt gold initially and produced over 1.2 million ounces of gold, so Carlin type deposits in the Bald Mountain district should not be discounted.

 

Details

01/20/2022 18:00:0001/20/2022 20:00:00America/Los_AngelesGSN Elko Chapter MeetingThis month’s GSN Elko Chapter meeting will be held at the Western Folk Life Center on Thursday, January 20, 2022
After four months of hybrid talks with varying degrees of success in our virtual presentation component, with plenty of frustration by both our volunteer officers and virtual attendees voicing their displeasure with audio/visual quality we will be returning to 100% in person presentations in 2022. So please attend if you want to enjoy the presentation, soak up some knowledge, suds, and social merriment.
Thursday, January 20th Food and drinks @ 6 pm and talk to begin at 7 pm. Presenter: David R. Ernst, Exploration Manager for Kinross - Bald Mountain Title: Bald Mountain District Geology, White Pine County, Nevada  Abstract:  The Bald Mountain District is located on the southeast extension of the Carlin Trend at the southern end of the Ruby Mountains in White Pine County, Nevada. The district has produced over 6 million ounces of gold and has a resource of nearly 6 million ounces of gold.  The property covers over 131,000 acres and is considered the largest contiguous land position in the United States. The first claims in the district were staked in 1869 in the northern portion of the district and modern exploration for gold has been conducted for over forty-five years. Outcropping ore-bodies were discovered long ago. Current efforts focus on prospective areas covered by post-mineral volcanics and/or alluvium, areas that were neglected due to low grade drill results, and areas where poor host rocks may hide deposits in permissive stratigraphic horizons. Where possible, structural intersections at permissive host rock horizons are targeted. Two gold mineralizing events occurred at Bald Mountain: Jurassic-age intrusive-related and Eocene-age sediment-hosted. During the Middle Jurassic Period,  gold deposits formed on the margins of intrusive bodies. The Jurassic-aged Bald Mountain Stock and intrusive-related deposits occur along a broad structural zone trending northwest from the Bida deposit through Top to Redbird/Numbers. This structural zone is called the Bida Trend. Gold mineralization is concentrated on the NW and SE ends of the stock, especially at the intersection of the Bida Trend with a major structural corridor bounded by the Dynasty and West Top Faults. These deposits are hosted by several sedimentary units ranging in age from Cambrian to Mississippian. At Top, units that host the majority of the gold are the Cambrian Windfall and Ordovician Pogonip Formations, and Jurassic intrusives. The deposit dips moderately to the east to northeast and is open at depth. In general, intrusion-related deposits are deeply oxidized, and at Top, oxidation extends to over 2500 feet below the surface. The second mineralizing event occurred in the Eocene. This younger event produced gold mineralization and deposits that are similar to the gold deposits at Carlin in that they are sediment-hosted and disseminated. Carlin type deposits occur in specific horizons at the top of the Devonian Guilmette Limestone, in the Mississippian Pilot Formation, or in Joana Limestone and the base of the Chainman Formation. The best host rocks are formations with silt/sand grains with carbonate (calcite or dolomite) cement. Where the intrusive-related deposits appear to be overprinted by Carlin type deposits, we have hybrid deposits.  There are thick parts of the stratigraphic section that make poor hosts, specifically massive sections of limestone and dolomite. In some target areas, these sections of barren rock can hide gold-bearing zones below. Deposits occur where rocks are strongly deformed along faults and fault intersections, especially in the permissive host rock horizons. Structural intersections at permissive host rock horizons are targets for exploration. The important structural trends that control mineralization in the district are: NNE, NW, NNW, and WSW. Low-angle structures, both compressional and extensional, and folds can also be important. The structural evolution in northern Nevada is complex. Several tectonic episodes have deformed and displaced the stratigraphic units in the region and many faults have been reactivated at various times as stress regimes have changed. Post-mineral deformation was extensional. This tectonism formed the Great Basin’s basin and range physiographic province that exists today and has affected the rocks and gold deposits at Bald Mountain. Some of the displacement appears to be lateral along strike-slip or oblique-slip faulting. The two deposit types have different chemistry. Intrusive-related deposits have a trace element signature of Cu, Ag, Mo, Bi, Te (As and Sb) while the Carlin type systems have As, Sb, Hg, Tl. Intrusive-related deposits contain high grades locally and coarser gold while the Carlin systems have fine-grained gold that is more evenly disseminated. Oxidation and the refractory nature of carbon in the ores are different in the two deposit types. Carbon is not always refractory or preg robbing in the intrusive-related deposits while carbonaceous, sulfide bearing material in the Carlin type deposits is refractory. Copper can be an issue in intrusive-related deposits because it competes with gold in reaction to cyanide. The size and grade of the two deposit types is a consideration because the intrusive-related deposits tend to be larger and higher grade. However, Vantage is a Carlin type deposit that averaged 4 gpt gold initially and produced over 1.2 million ounces of gold, so Carlin type deposits in the Bald Mountain district should not be discounted.  
Reno, NV
Event StartsEvent Ends
01/20/202201/20/2022
All Day Event
6:00pm8:00pm