Mining Intelligence and News
United States

South Railroad Project

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Mine TypeOpen Pit
  • Gold
  • Silver
Mining Method
  • Truck & Shovel / Loader
Mine Life... Lock
SnapshotThe South Railroad project consists of the Dark Star and Pinion deposits and is situated within a prospective land package along the Carlin trend.

Gold Standard conducted environmental baseline studies over the past several years as part of their ongoing permitting efforts and in preparation for the submittal of permit applications for conduct mining operations.

The United States Bureau of Land Management (BLM) has determined that the review and approval process for the Plan Application requires an EIS, due to the mine dewatering and potential pit lake.The Orla Mining will also need an Individual Section 404 Permit from the United States Army Corps of Engineers, and this agency will be a cooperating agency on the NEPA documents. As of the December 31 2023, the Notice of Intent is with the BLM for review. The Orla Mining expects the Notice of Intent to be filed in the Federal Register in 2024.


Orla Mining Ltd. 100 % Indirect
Gold Standard Ventures Corp. owns 100% of the South Railroad project.

On August 12, 2022, Orla Mining Ltd. completed the previously announced acquisition of Gold Standard by way of court-approved plan of arrangement (the "Transaction"). As a result of the completion of the Transaction, Orla acquired all of the issued and outstanding Gold Standard Shares and Gold Standard became a wholly-owned subsidiary of Orla.



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Deposit type

  • Carlin-type


The Railroad-Pinion property includes demonstrated Carlin-type gold mineralization in at least four deposit areas: North Bullion, Pinion, Dark Star, and Jasperoid Wash. These deposits are similar in setting and style to that of other deposits in the region, including Rain and Emigrant (Koehler et al., 2014; Norby et al., 2015; Turner et al., 2015; Dufresne and Koehler, 2016). Mineralization occurs mainly as finely disseminated, submicroscopic gold in largely stratiform bodies in Devonian, Mississippian, and Pennsylvanian- Permian rocks. The following subsections describe the mineralization in the North Bullion, Pinion, Dark Star, and Jasperoid Wash deposits and are modified from Dufresne and Nicholls (2016; 2017a; 2017b; and 2018).

The Railroad-Pinion property has two adjacent parts, the North Railroad portion (“North Railroad”), which includes POD, Sweet Hollow, and North Bullion (collectively called the North Bullion deposits, or the North Bullion area), and the South Railroad portion (“South Railroad”), which includes Dark Star, Pinion, and Jasperoid Wash.

North Bullion Deposits
The North Bullion deposits, which includes North Bullion, POD, Sweet Hollow and South Lodes zones, contains Carlin-type disseminated-gold mineralization that is largely not exposed at the surface. The bulk of the geological understanding and interpretation of the North Bullion deposits has come from core drilling that was guided by interpretations of gravity and CSAMT data. Gold mineralization is focused in the footwall of the NBFZ, a north-south striking zone of normal faults with an overall down-to-the-east displacement. North-south-, northwest-, west-northwest-, and northeast-striking faults appear to be important controls on mineralization.

The upper limit of gold mineralization at the North Bullion deposit varies from 350 ft to 1300 ft (105 m to 400 m) in depth. The dip of the mineralized material steepens from 10° to 45° to the east as the eastern strand of the NBFZ is approached. Gold is associated with sooty-looking, very fine-grained sulfide minerals, silica, carbon, clay, barite, realgar, and orpiment in addition to elevated arsenic, mercury, antimony, and thallium. Gold grades >0.175 oz Au/ton (>6 g Au/t) have been intercepted.

The North Bullion deposit, as currently defined, is approximately 2,500 ft (750 m) in length, 2,000 ft (600 m) in width and as much as 1,650 ft (500 m) in vertical extent.

Mineralization at the nearby POD zone is restricted to a steeply dipping shear zone which trends west-northwest and is situated in rocks stratigraphically higher than the lower mineralization at North Bullion (Hunsaker, 2012b; Masters 2003). Mineralization at POD is hosted by the upper siltstones of the Webb Formation. The core of the mineralized body contains carbon and fine-grained, disseminated pyrite, and accounts for approximately 15% of the mineralization. This is surrounded by strongly oxidized mineralization. Gold grains are in the range of 5 to 20 microns, and are associated with oxidized pyrite, stibnite, and arsenopyrite (Masters, 2003). Additionally, gold mineralization at POD is associated with silicified rock, including jasperoid, argillized rock, pyrite, barite, and some minor dolomite replacement of calcite (Hunsaker, 2012b).

As currently defined, the POD zone is approximately 2,100 ft (650 m) in length, 500 ft (150 m) in width, and as much as 650 ft (200 m) in vertical extent.

The Sweet Hollow zone is situated about 650 ft (200 m) southeast of the POD zone and about 2,000 ft (600 m) south of the North Bullion deposit. As currently defined, the Sweet Hollow zone is approximately 3,500 ft (1,050 m) in length, 800 ft (250 m) in width, and as much as 330 ft (100 m) in vertical extent.

Pinion Deposit
The Pinion gold deposit is located along the west-northwest-trending Pinion anticline and proximal to the Bullion fault. The Main zone trends approximately N50°W to N60°W, is approximately 3,300 ft long by 3,300 ft wide (1,000 m by 1,000 m), and varies in thickness between ~50 to 500 ft (~15 to 150 m) vertically. Mineralization at the Main zone has been intersected to a depth of 650 ft (200 m) below surface. Mineralization is hosted primarily along the crest of the Pinion anticline, but also along the east and west limbs. The multi-lithic dissolution-collapse breccia at the Devils GateTripon Pass contact hosts the majority of mineralization, with minor amounts associated with decalcified limestone and dolostone above and below the breccia.

The North zone is approximately 3,600 ft (1,100) m long, along a roughly north-northwest trend, varies from 150 ft to 330 ft (45 m to 100 m) in width, and ranges from 115 ft to 440 ft (35 m to 135 m) in vertical thickness. Mineralization at the North zone is hosted primarily in multi-lithic breccia and appears to be an offset of the east limb of the anticline. Low-grade mineralization has also been noted in the Sentinel Mountain Dolomite.

Mineralization at Pinion occurs mainly as submicroscopic disseminated gold in the largely stratiform, multi-lithic, dissolution-collapse breccia developed along the contact between silty micrite of the Tripon Pass Formation and calcarenite of the underlying Devils Gate Limestone. Important structural controls are west-northwest and north- to northeast-striking folds and faults. Gold deposition is thought to have been contemporaneous with breccia development and with quartz vein formation and silica ± barite replacement and infill of open spaces. Some free gold in 2 to 20 micron-size grains has been noted in 2018 mineral liberation studies (AMTEL, 2018). Barite was deposited as both massive and disseminated forms and is found most often in the multi-lithic, dissolution-collapse breccia. Barite appears to be paragenetically late, overprinting both the breccia and silica events.

Dark Star Deposit
The Dark Star deposit is hosted primarily within Pennsylvanian-Permian undifferentiated units possibly equivalent to the Tomera Formation, with minor amounts of gold mineralization found in the Chainman Formation. The deposit is centered along the north-south-striking Dark Star fault corridor and is elongate in the N5°E direction. As presently defined by drilling, the deposit consists of the Dark Star Main and Dark Star North zones, and has dimensions of approximately 4,600 ft (1,400 m) in length, up to 2,300 ft (700 m) in width, and to a depth of 1,500 ft (450 m) below surface.

Gold mineralization at Dark Star is submicroscopic and disseminated within a north- to north- northeast-striking zone of silicification within the middle coarse conglomeratic and bioclastic limestone-bearing unit. This unit is between the upper and lower silty limestone and calcisiltite units. At Dark Star Main the mineralization dips steeply to the west near the surface to sub- horizontal at depth; at Dark Star North the mineralization dips steeply to the west.

Oxidation is pervasive at Dark Star Main to a depth of 1,500 ft (450 m) in the middle conglomeratic unit. At Dark Star North, oxidation is pervasive to a depth of 1,100 ft (330 m) in the middle conglomeratic and lower silty limestone and calcisiltite units. Oxidation products are primarily limonite with lesser hematite. However, thin zones of unoxidized sulfide minerals are present; pyrite is the principal sulfide mineral.

Jasperoid Wash Deposit
The Jasperoid Wash deposit has approximate extents of 1,400 m in a north direction and a width of about 1,100 m. Drilling shows the deposit dips west gently to steeply at least 400 m. Gold is disseminated within altered feldspar porphyry dikes and adjacent conglomeratic rocks, possibly the same units that host mineralization at Dark Star. The gold is inferred to be submicroscopic, though no petrographic studies have been done.



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Mining Methods


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Crushers and Mills

Milling equipment has not been reported.



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CommodityProductUnitsAvg. AnnualLOM
Gold Payable metal koz 1,030
Gold Metal in doré koz 1241,031
Silver Payable metal koz 644
Silver Metal in doré koz 651

Operational metrics

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* According to 2022 study.

Production Costs

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* According to 2022 study / presentation.
** Net of By-Product.

Operating Costs

OP mining costs ($/t mined) USD 1.52 *  
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* According to 2022 study.

Project Costs

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Processing OpEx $M USD 147.4
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G&A costs $M USD 37.8
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Mine Management

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