Projects

Show printable version of 'Briggs' item in a New Window
Email 'Briggs' item to a friend

Briggs Gold Mine

 

The Briggs gold property ("Briggs") was acquired by the Company in 1990. Briggs was initially constructed in 1995; production ceased in 2004 due to gold-market conditions, and commercial production recommenced in mid-2009.  Briggs is a conventional open-pit mine that uses heap-leach gold recovery.  Targeted gold recovery is 80 percent. Briggs is located on the west side of the Panamint Range near Death Valley, California.  No royalties are payable at Briggs. All of the mining claims are located on land administered by the Bureau of Land Management ("BLM").


The Briggs Mine, NI 43-101 Technical Report dated May 22nd, 2012 increased mine life by two. Mining is now expected to continue at Briggs through the second half of 2016. 

View, NI 43-101 Technical Report

The report details an estimate of mineral reserves and mineral resources, which are summarized in the tables below.

Mineral Reserves 

Category

Tons (1,000)

Gold -- oz/ton

Contained Gold Ounces

Proven

4,536

0.020

89,281

Probable

4,753

0.020

94,170

Total

9,290

0.020

183,451

Briggs mineral reserve summary is based on a 0.007 oz/ton incremental leach cut-off grade calculated using $1,490 per ounce gold, and is supported by the NI 43-101 Technical Report dated May 29,2012 filed on SEDAR (see notes to the resource table below for additional information on the supporting Technical Report). These reserves were updated by Michael J. Read, SME-RM, of Chlumsky, Armbrust & Meyer LLC an independent, consulting engineer and Qualified Person as defined by NI 43-101. The reserves are reconciled for mine production in 2012 and are current as of December 31, 2012.


 

Estimate of Resource 

Category

Tons

Gold Grade

Contained Ounces

 

(oz/ton)

(Ounces)

Measured

10,358

0.021

214,500

Indicated

20,293

0.019

383,700

Measured &
   Indicated

30,651

0.020

598,222

Inferred

12,940

0.018

228,600

Mineral Resources for Briggs, Reward and Pinson Underground include Proven and Probable Reserves.

The resource is calculated based upon a 0.006 oz/ton gold cut-off.

The Briggs Mine mineral resource is supported by the report entitled "2012 NI 43-101 Technical Report Briggs Mine, Inyo County, California", dated May 29, 2012;  and filed on SEDAR on May 29,  2012 prepared by Alan C. Noble, P.E. of Ore Reserves Engineering, Michael J. Read, SME-RM of Chlumsky, Armbrust & Meyer LLC, William R. Stanley, SME-RM, V.P. Exploration of the Company, and Douglas E. Stewart, P.E., V.P. and COO of the Company.  Messrs. Noble and Read are independent qualified persons in accordance with NI 43-101 and Messrs. Stanley and Stewart are non-independent qualified persons in accordance with NI 43-101. 

Definitions used are consistent with those adopted by the Canadian Institute of Mining, Metallurgy and Petroleum ("CIM") Council in December 2005, as amended, and prescribed by the Canadian Securities Administrators' National Instrument 43-101 and Form 43-101F1, Standards of Disclosure for Mineral Projects. The measured and indicated resources stated above include reserves, which are a sub-set of resources. Mineral resources that are not mineral reserves do not have demonstrated economic viability. Inferred resources are considered too speculative geologically to have the economic considerations applied to them that would enable them to be categorized as mineral reserves.
 

Briggs Exploration

In late 2008 and into 2009, Atna evaluated exploration targets that may extend the project's mine-life. One of the targets, the Briggs Main Deep ("BMD") zone has now been cut by 22 drill holes. With the completion of the second phase of drilling, mineralization has now been intersected in drill holes over a north-south distance of 1,000 feet and an east-west distance of 750 feet. Atna is currently modeling the BMD zone to estimate the tonnage and grade of the new mineralization. Thickness of the sub-horizontal mineralized zone varies significantly within the drilled area ranging from 25 feet in the southern most intercepts to over 250 feet in the northern portion of the zone. The BMD mineralization remains open to the east and north.The mineralization comes within 40 to 50 feet of the $750 ounce per gold design pit bottom. The BMD remains open for expansion to the north, south and east of the current intercepts.

Briggs Main Deep 3D video showing mineralized zone, drill hole intercepts and current planned pit design.
Briggs Main Deep 3D Image

Outside of the Briggs Mine permit area, Atna controls four exploration targets; Cecil R, Suitcase, Mineral Hill and Jackson, all within the Briggs area claim block. All of these projects have seen significant drilling and have historic mineral inventories; however the Cecil R property is the most advanced of these projects.

In February 2009, Atna completed a 23 hole program at the Cecil R project bringing the drill hole total at the project to 94 holes (21,956 feet). The program successfully extended mineralization 700 feet to the south and defined the western and eastern limits of the mineralization within the known mineral horizon.


 

Briggs Mine Photo Gallery
Click to view a selection of photos from Briggs Mine.

 

Briggs History and Geology

The Briggs Mine is located in Inyo County, California about 50 miles east of the town of Ridgecrest, California. The Briggs property consists of 198 unpatented and two patented mining lode claims, and one patented and 18 unpatented millsite claims that together cover a total area of approximately 4,480 acres.

The Panamint Mountains trend north-northwest for approximately 80 miles and average about 16 miles in width. The range is flanked by the grabens of the Panamint Valley on the west and Death Valley on the east. The western flank of the Panamint Range is underlain by rocks that vary in age from Precambrian to recent and that have been modified by several tectonic and metamorphic events. The rocks have been deformed by at least two folding episodes and were intruded during the mid-Mesozoic time by granitic to dioritic intrusions. Shearing and hydrothermal activity focused in low-angle structures as well as vertical extensional fault zones, depositing silica, Ca-Mg-Fe carbonates (silica-carbonate alteration), and pyrite with gold and traces of chalcopyrite.

Both gold mineralization and wall rock alteration are controlled by large-scale and micro-scale structures. They are responsible for rock preparation of an otherwise generally unsuitable host in the form of the quartz-feldspar gneiss. The most obvious structure, the Goldtooth fault, was a major conduit for ore-bearing fluids. The Briggs ore bodies are disseminated replacement style deposits. The alteration-mineralization displays a remarkably simple assemblage of gold, disseminated pyrite, carbonate (usually ferroan dolomite), and silica (+/-) sericite. Styles range from broadly disseminated at Briggs Main and Briggs North to structurally controlled and partially replaced host rock at Gold Tooth and Briggs North underground.

The Briggs drill-hole database consists of 985 drill holes (including 71 holes at Cecil-R and 34 holes at the Jackson areas) with a total footage of 28,543.3 feet drilled at Briggs, 22,056 feet drilled at Cecil-R, and 14,162 feet at the Jackson prospect. Cecil-R and Jackson are located to the north of Briggs.

From 1996 to 2004, Briggs produced gold by heap leaching both crushed and uncrushed (run-of-mine) material placed on leach pads. A total of 23.5 million tons of material grading 0.031 oz Au/t containing nearly 740,000 ounces of gold was placed on the leach pads. A total of 51.6 million tons of waste have been mined, indicating an overall stripping ratio of 2.186:1 over the life of the mine.

The Briggs Mine gold recovery process is conventional heap leach. Crushed or run-of-mine ore is placed on the leach pads and leach solution is recirculated between the ore and the gold adsorption recovery columns. Gold is adsorbed onto the carbon and then desorbed from the carbon into a stripping solution. Electrowinning removes the gold from the stripping solution onto stainless steel mesh, forming sludge. The sludge is then smelted and refined into gold doré and sold. The Briggs refinery typically produces a doré of 70% gold and 20% silver.

The information presented on this web page was prepared under the supervision and review of William Stanley, V.P. Exploration of Atna, a Registered Member of the Society for Mining, Metallurgy, and Exploration, a Licensed Geologist and Qualified Person, as defined in NI 43-101, and has verified the authenticity and validity of the technical information contained herein.