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 Yukon: A Brief Photo Tour

Today's post has some of my favorite photos from the wild and scenic Yukon Territory of Canada.  It is a wonderful place for a vacation.  It is so popular with German tourists that there are non-stop flights from Frankfurt to Whitehorse.  The Japanese are also common visitors to the Yukon.

 

Map from the Yukon Travel website.  The site is an excellent website for planning a trip to the Yukon.  The link is below.

 

Source of Map Yukon Travel Website

 

 

Plaque memorializing the early prospectors making their way over Chilkoot Pass.

Helicopter with the Yukon River in the background, fire weed, placer gold nuggets mined by modern-day, small miners, and abandoned exploration and mining equipment (1970's Ford Bronco).

 

 

Photo of large landslide on the south side of Little Salmon Lake between Carmacks and Faro (photo date August 7, 2012).  Oblique view of landslide from Google Earth (lower left),  vertical Google Earth image (north is up).  The arrow shows the approximate location and direction of the photo of the landslide taken from Highway 4.  Google Earth images from 2004 through 2008 show that the slide develop and moved over a 5-year period.

 

 

The beauty of the Yukon and a bear footprint next to a rock hammer.

  

Majestic mountains in the southeastern area of the Yukon looking towards the Northwest Territories.

 

The Yukon River at sunset.

 



Gold Discovery: 10 Basic items needed for a successful transition from exploration to a mine.

I dug up an old memo written in 1983 by Neil Muncaster, Vice President of Exploration for Tenneco Minerals Company.  I worked for Neil in the mid-to-late 1980's.  At that time most geologists, especially exploration geologists, did not use computers.  He commented to me that if he had a geologist using a computer to contour geochem or other assay data he would fire them.  He also wanted to see individual assays on cross sections, not composites or mineralized intercepts.  Mostly he was a ore finder, whether directly or in managing exploration departments as the VP.

This is a copy of that brief memo...

 

 

The memo is rather dated.  Now with GPS and GIS geologists routinely have real-world coordinates.  Software like Leapfrog https://www.leapfrog3d.com/  and GeoReka  http://www.geo-reka.com/ puts high tech computer modelling in the hands of exploration geologists. 

 

It has been my experience that the greatest weakness in exploration "discoveries" is the lack of early metallurgical testing.  Hot cyanide assays and bottle roll test for gold extraction are inexpensive and should be done a soon as ore-grade intercepts are made.

 

This is a good check list for projects that have ore-grade intercepts and for projects just getting started.  Best of luck with your drilling projects!

Nevada Gold: Hoping for better times in 2017

To all of my friends and Nevada geo's, here is to hoping that 2017 brings higher gold prices and VG in your rock samples!

Coarse, crystalline gold from Nevada, about 1.2 troy ozs.

Empire Mine State Park, Grass Valley, CA

Greetings from Reno,

I am sure that many of you that live in Reno, Sacramento, or the Bay area have visited the Empire Mine State Park located in Grass Valley and adjacent to Highway 49.  But, for those of you that have not, it is well worth taking in this wonderful outing!

The park's website is http://www.empiremine.org/

The Empire is an underground mine which produced gold from 1850 until 1956, with a few years suspension of production during World War II.  The total gold production from the Empire and other gold mines in the Grass Valley and Nevada Districts is approximately 12 million troy ounces.

Gold was discovered in June 1850 by George McKnight at the Gold Hill Ledge.  The discovery was of a quartz vein filled with abundant visible gold.  The Empire and nearby North Star mine operated profitably until the late 1920's when it was less profitable owing to increased costs.  In 1929, Newmont purchased the Empire mine from W.B. Bourn for $250,000.  Newmont also acquired the North Star mine.  In 1929, the gold price was $20.67 per ounce, but in 1934 to gold price was set at $35 per ounce.  Overnight, this turned a marginal mine into a highly profitable mine.  The mine closed in 1956 when the costs exceeded the sales.  In December 1974, the State of California purchased the property from Newmont for $1,250,000. The park is a treasure for geologists, mining enthusiasts, historians, and those that love beautiful landscaping and buildings. Source:  McQuiston Jr., F.W., 1986, Gold:  The Saga of the Empire Mine 1850-1956, 95 p.

Highlights of the park include beautiful grounds with flower gardens, the mine owner's mansion, fountains, a small museum, mine buildings, an inclined shaft (12,000 feet deep on the incline), a large model of the mine workings and geology, and ore carts.

I hope that some of you get a chance to visit the Empire mine and park.




The Empire mine mansion.



Ore carts at the mine.

The inclined shaft at the Empire mine.

Mine model.

Ore sample of gold-bearing quartz, probably similar to the discovery outcrop at Gold Hill!

A New Blog on Gold Exploration and Geology

Hello Bloggers and Geo's,

I am a recently retired exploration and mine geologist; mostly for gold and living in Reno.  My retirement comes after 40 years of banging on rocks!  Like all industries it has had its ups and downs.  Hopefully the current downturn will end in a couple of years.

A few times a week, I plan to share some of my experiences, photos and maybe some maps from my work.  And, some of the lessons that I have learned and mistakes that I have made.

This is my first venture into the BLOGOSPHERE!

Signing off for now,

Geo Gold Emmons

Adventures in Borneo 1993 (Blogger in center)



Abandoned Gold Dredge about 100 km south of the Klondike District