1986 Field Trip to the Fortitude Gold-Silver Mine, NV

In May 1986, I was working for Tenneco Minerals Company as an exploration geologist and visited the Fortitude gold skarn deposit in the Battle Mountain Range in Nevada. The deposit was owned by Battle Mountain Gold Corp. (BMG). The mine visit was part of a field trip part of GEOEXPO/86. The trips were add-ons to a symposium held in Vancouver, BC. The trip and symposium were sponsored by The Association of Exploration Geochemists and Geological Association of Canada. The field trips were lead by Harold (Hal) F. Bonham of the Nevada Bureau of Mines and Geology.

View northerly of the Fortitude open pit from August 1986 (Emmons).

One month earlier, July 1986, three Battle Mountain geologists: P.R. Wotruba, R.G. Benson, and K.W. Schmidt published a brief but informative description of the Fortitude deposit (Battle Mountain describes the geology of its Fortitude gold-silver deposit at Copper Canyon: Mining Engineering, p. 495-499). The benches are 20 feet high for scale.

This cross section of the Fortitude is from the above cited paper by Wotruba, et al. and the following description of the geology is summarized from the paper.




Fortitude gold-silver, sulfide-skarn deposit cross section looking due north by Battle Mountain Gold Corp. 1986.

The reserves reported by BMG in January 1985 were 11 million tons grading 0.154 opt gold and 0.83 opt silver containing 1.7 million ounces of gold and 9 million ounces of silver.

The gold-silver skarn deposit is located in the Copper Canyon area of the Battle Mountain Range. The center of the mineralized zone is occupied by an altered granodiorite pluton (Eocene, radiometric date of 38.5 Ma). An altered dike extends to the north from the Copper Canyon pluton and fills the Virgin fault. Hydrothermal alteration and metal zoning form concentric shells around the intrusion. The inner zone of alteration is potassic altering the granodiorite. The limit of this alteration is defined the limit of secondary biotite. Further out is phyllic and then propylitic alteration. Metal zoning outwards from the intrusion is: Cu+Au+Ag > Au+Ag > Pb+Zn+Ag. Fluid inclusion data indicate temperatures of >500 to 200 degrees centigrade.

The sulfide skarn is hosted by the Antler Peak Limestone (Pennsylvanian).  The deposit is stratabound (manto-like) and is distal to the source intrusion in Copper Canyon. The limestone occurs within other carbonate and clastic rocks of Permian and Pennsylvanian age. Thrust over these strata is the Havallah (previously called the Pumpernickel) sequence. The Golconda thrust is related to the Sonoma orogeny.

The mineralogy of the skarn consist of andraditic garnet, diopside, epidote, actinolite, tremolite, quartz and calcite. Sulfide mineral consist of pyrrhotite, chalcopyrite, pyrite, sphalerite, and galena. Sulfide content is locally of a massive nature. Owing to the pyrrhotite content the mineralization is magnetic and was reflected in a small aeromagnetic anomaly. This was part of the discovery story of the Fortitude deposit.

Gold Specimens from the Round Mountain Mine, Nevada

The Round Mountain gold deposit is located in central Nevada and is a low-grade, disseminated gold deposit. The mineralization is hosted by Tertiary rhyolite tuff and Paleozoic metasedimentary rocks. The deposit was discovered in the early 1900s by local prospectors. The discovery included a multi-pound gold "nugget" that was found at a badger hole on the flank of the hill of Round Mountain. Early production was by placer, open cut and underground mining. Modern production began in 1977 and continues today (2019) by open pit mining with the gold recovered by heap leaching and milling.

The mine is currently owned and operated by Round Mountain Mining Corp., a wholly owned subsidiary of Kinross Gold Corp. The gold production since 1977 exceeds 15 million troy ounces.

The Round Mountain deposit is unique in the quality of coarse, crystalline gold (electrum) specimens that it has yielded. These are a few examples of the gold from the author's collection.


Coarse gold veining with quartz vein cutting a hydrothermally altered rhyolite tuff. The vein with adularia is 26.0 Ma
and the rhyolite tuff is 26.5 Ma



Coarse gold associated with intense quartz-adularia (potassic) alteration in the non-welded pumice tuff of Round Mountain.



Crystalline gold in quartz +/- adularia vein hosted
by Paleozoic metasedimentary rocks.




Coarse crystalline gold "nugget" 
approximately 1.3 troy ounces (electrum.) 



For more information on the Round Mountain gold mine just Google it and for a satellite image search for "Round Mountain, Nevada" in Google Earth.

Wall Canyon, Nye Co., NV: Isoclinal and recumbant folds

A cliff face on the south side of Wall Canyon in the Toiyabe Range is an excellent exposure of early Paleozoic sedimentary rocks tightly folded into recumbent and isoclinal folds and thrust faults.


Photo of south cliff face in Wall Canyon, Photo courtesy of Paul Klipfel consulting geologist, Reno, Nevada. [Annotations by the Blogger]
Website:  www.mineralresourceservices.com

Location map of Wall Canyon, Nye Co., Nevada

Oblique Google Earth view of south side of Wall Canyon, southerly view.

Geologic map of Wall Canyon area.  USGS 1954, Ferguson and Cathcart, Round Mountain Quad,GQ-40.

If you are driving between Tonopah and Austin it is worth a short side trip to see folds for yourself.   A great photo opportunity!

iPhone App: Photos with GPS Coordinates and Map

There is an App that every field geologist should have, it is called "Theodolite."

It runs on iPhones and other smart phones in addition to iPads.

The App captures a photo and also records the coordinates, viewing direction and you can add notes to the photo. It stores a non-annotated photo too. It also shows location on a map.

Link to Website of Theodolite

These are some screen shots from their website.

The App can record the coordinates in several different projections with add on it can even record coordinates in State Plane. You will need to calibrate the compass on the iPhone so that it reads directions to True North.

Geology and Ore Deposit Stamps - South Africa

Earlier this year someone posted this on Linked In; stamps showing beautiful cross sections of ten ore deposits of South Africa.

Geology as Art

Geology Poster of the Geologic Cross Sections Stamps

Plate Block of the Stamps

Mineral Stamps from Africa

Too bad America doesn't know the importance of minerals.  But enjoy following the link.

Link to Geology Stamps from South Africa

Jamestown Gold Mine, CA: Mother Lode Exposed in Open Pit

 

In April 1992, I toured the Jamestown mine that is adjacent to Highway 49 in the Mother Lode district of California.  I snapped a photo of the southern highwall of the pit.  The mine was called the "Harvard Pit."



USGS 71/2' topo of the Jamestown area.

 

 

Google Earth image of the Jamestown area (Image May 2017)

I snapped this photo in 1992 of the highwall of the pit.  The mine was called the "Harvard Pit."

Harvard pit looking southeasterly.

Geologic sketch of the Harvard pit showing the pit lake.  Source:  Savage, Ashley, Bird, 2000 +/-, Geology of the Jamestown mine, Mother Lode gold district CA, and geochemistry of the Harvard mine pit lake, USGS.
Source:  Link to PDF of Presentation

 Harvard, Crystalline, and Alabama mines

• Discovered in 1848 placers and 1850 lodes.
• Major production from 1890 to 1916
• Gold produced was 110,000 to 160,000 troy ounces (grade 1.0 to 1.4 opt)
• Ore processed 330,000 to 1,100,000 tons

 

Jamestown mine (Harvard pit)

 

• Exploration periods 1938 to 1942 with the increased gold price and 1974 to 1985.
• Mining and processing from 1986 to 1994.
• 660,000 troy ounces produced.
• Ore processed 10,500,000 tons.
• Recovered grade 0.063 opt.
• Stripping ratio >4.15:1
• Largest "nugget" gold  recovered 876 troy ounces (lode gold not placer).

Source:  Savage, et.al.



 

Hanging wall:  Graphitic slate, metavolcanics. Quartz, albite, chlorite, sericite, graphite, ferroan dolomite, pyrite.

Ore Zone:  Sheared fragments of hang wall and footwall rocks and quartz veins.  Quartz, albite, mariposite, chlorite, sericite, talc, ferroan dolomite, magnesite, calcite, arsenian pyrite, native gold, sulfosalts, Au-Ag tellurides.

Footwall:  Altered serpentinite, diorite, gabbro.  Talc, tremolite, actinolite, chlorite, chromite, magnesite, gersdorffite, niccolite, millerite, colbaltite.

Gossan:  Goethite, magnesiocopiapite, jarosite, gypsum, hexahydrite.

Source:  Savage et.al.

The Cove Open Pit Au-Ag Mine and Anticline, Nevada

I found a photo that I snapped in October 2000 of the Cove pit showing the well exposed anticline.  October 2000 was the last month of open pit mining at the Cove. The anticline is no longer visible owing to the pit lake. It is great to see classic geological structures exposed in open pits, so I am posting it so that others can see the annotated photo.

The orebody is largely controlled by the crest of the anticline and favorable stratigraphic units of the Augusta Mountain Formation (Triassic). Three members of the formation are exposed in this view of the pit.  In addition one of the Eocene felsic dikes filling a fault shows up as the light colored linear that stair steps through the benches. The post mineral Tuff of Cove Mine fills the erosional trough that is superimposed on the axis of the anticline owing to fracturing and hydrothermal alteration.

Premier Gold Mines Ltd. continues to explore the Cove/McCoy area and has had some significant intercepts of gold and silver at depths suitable for underground mining.

They released new (April 15, 2017) a technical report on the project. It is available on their website via this link:  NI 43-101 McCoy-Cove Project, NV  This excellent report is on the McCoy-Cove mineralization, the geology of the deposits and the current status of their exploration.

From Page 6-6 of their technical report, the total production from McCoy and Cove from 1986 through 2006 was 3.41 M ozs of gold and 110.2 M ozs of silver. The vast majority of the silver is from the Cove deposit and approximately 2.6 M ozs of gold is attributed the Cove deposit.