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.

Brief History of the Theory of Plate Tectonics

I stumbled across my copy of the book Principles of Physical Geology written by Arthur Holmes in 1944.  He wrote the book while Professor of Geology and Mineralogy at the University of Edinburgh. It is interesting that he wrote the book in the United Kingdom during World War II.  The final chapter is on Continental Drift which is now called Plate Tectonics.  He discusses the work of Alfred Wegener in the early 1900's and includes some of Wegner's reconstruction of the continents through geologic time.  The final section is on the search for the mechanism for continental drift.  He put forth the idea of convection cells a mechanism for the drift of the continents.  He includes two cross section depicting the convection cells.  One section shows the mid-oceanic ridges as spreading centers creating new oceans.  It doesn't appear that he understood subduction zones.

It wasn't until the 1960's and 1970's that science proved that Wegener and Holmes were largely correct with their theory.  It required new technology to uncover the "secrets" of plate tectonics:  mapping of the ocean floors, marine magnetic surveys (using instruments designed in World War II to search for submarines), the discovery of the reversals of the earth's magnetic field, paleo magnetism, recognition that the mid-ocean ridges are spreading centers, a global network of sensors in the 1960's for the Nuclear Test-Ban Treaty of 1963, and deep sea core samples from the Glomar Challenger.

Dust jacket of Holmes' geology textbook.

 

Holmes' chapter on Continental Drift.

 

Wegener's reconstruction to the continents in Late Carboniferous, Eocene and Early Pleistocene (from Holmes,1944).

  

The cross sections from Holmes' chapter on Continental Drift.

Key Events in the Formation of the Theory of Plate Tectonics

• 1596 Abraham Ortelius recognized that the coast of the Americas and Europe and Africa appear to have been joined a sometime and then pulled apart.
• 1912 Alfred Wegner hypothesized that the continents had a onetime all been joined together.  He named the super continent Pangea.  He termed the process continental displacement.  Unfortunately during his lifetime the theory was not accepted by the scientific community.
• 1929 Arthur Holmes proposed that convection currents were mechanism of the movements of the continents and the formation of new oceans.
• 1950's  Mapping of the topographic features of the ocean floor reveals underwater mountain ranges in the mid oceans with great vertical relief and extending for thousands of miles.
• 1960  Harry H. Hess, American geophysicist, proposed the idea that oceanic crust forms was from the mid-ocean ridges and spreads laterally in opposite directions.
• 1961 Robert S. Dietz, American geophysicist, named Hess' process as sea floor spreading and further advanced the theory of plate tectonics. 
• 1963 Frederick J. Vine and Drummond H. Matthews, British geologists, and Laurence W. Morley, Canadian geophysicist, discovered the "magnetic strips" that symmetrically parallel the spreading centers at the oceanic ridges due to the paleo magnetism and reversals of the earth's magnetic poles.
• 1960's Global network of sensors it set up to detect nuclear tests as a result of the Nuclear Test-Ban Treaty signed in 1963.  The data revealed the pattern of earthquakes is concentrated along the continental edges.
• 1968 The ship Glomar Challenger collects core samples from the Atlantic ocean and reveals the age of the sediments increase in age away from the spreading centers.

 Source for the above section: Encyclopedia Britannica

 

Alfred Wegener (1880-1930

 

Screen capture from YouTube from The Amoeba People, a humorous take on Wegner's lack of scientific acceptance until decades after his death by freezing in the ice field of Greenland.  Harry H. Hess at the blackboard during a presentation.

 

Continental Drift: Alfred Wegner, The Amoeba People, YouTube

 

Arthur Holmes (1890-1965) Photo: 1912

 

Holmes published the second edition of Principles of Physical Geology in 1963. This when the concept of plate tectonics was becoming more widely accepted by the scientific community.  When he died in 1965 he was most remember for his working on radiometric dating and the geological time scale.  His work on plate tectonics as early as 1929 was largely forgotten.