Marigold has been described as a “distal-type sediment-hosted gold-silver deposit” by Theodore, (1998), being related to Eocene magmatism. Such deposits are similar to “Carlin-Type deposits”, but have been described as a sub-class or derivation of Carlin-Type deposits in the past 15 years, although the differences are subtle and the details of classification controversial in geologic literature. A deposit model for Au-Ag deposits in Northern Nevada that included information derived from the Property was created by Theodore (1998). In this model, the heat and potential metal source for Au-Ag bearing fluids is a porphyry intrusive. The metalliferous fluids sourced from or driven by the heat of the porphyry are deposited into favorable horizons and structural openings within sedimentary host-rocks, forming combined lode and manto-shaped orebodies.

The Marigold orebodies have certain characteristics of distal-type sediment-hosted gold deposits that are distinct from epithermal deposits and from the Au-Ag-Cu-skarn deposits such as the Fortitude and Phoenix deposits some 13 miles to the south east of Marigold. Key characteristics of distal-type sediment-hosted gold deposits include:
• Orebodies are replacement bodies without typical epithermal-style veins or epithermal open-space features;
• Gold and ore-stage sulfides are typically disseminated in sedimentary host rocks;
• There is no direct relationship between ores and an ore-stage major pluton, although there commonly are associated distal-type dikes and/or sills. Authors speculate that there is a major pluton at depth below such ore districts from which the dikes emanated;
• A trace-element association of Au-As-Sb-Hg that has less Cu-Ag-Pb-Zn-Bi than skarntype deposits;
• Typical hydrothermal alteration assemblages of jasperoidal silicification, argillization, and decalcification of carbonate-bearing lithologies, and a general lack of porphyry style alteration types such as potassic – phyllic – propylitic;
• There is a general lack of high-temperature contact-metamorphic calc-silicate mineralogy in these deposits, in contrast to skarns or skarn related orebodies (although some finegrained hornfels are present in some districts); and
• Ore controls useful for exploration include a common association with fold hinges, ores being aligned along favorable faults or fault corridors that were active during mineralization, the association with dikes, and a common lithologic control which can result in manto-like shapes to orebodies in chemically reactive host rocks. Orebodies in these deposits have been shown to be hosted by numerous lithologies, the common feature being some type of ore-stage permeability whether primary or secondary.

Gold mineralization is clearly restricted to fault zones and favorable stratigraphic horizons with the host rocks. In un-oxidized rocks, gold occurs in quartz veinlets within arsenic enriched overgrowths on pyrite and are interpreted to be of the same age as regional Eocene magmatism (Fithian et al., 2014).

Marigold uses a standard open pit mining method with a current mining rate of approximately 200,000 tonnes per day. The property undertakes conventional drilling and blasting activities with a free faced trim row blast to assure stable wall rock conditions.

Mining is done on 50 foot (15.2 meter) benches for pre-stripping waste and 25 foot (7.6 meter) benches for ore. Loading operations take place mainly with three primary loading shovels. Backup loading is done with a front end loader. Waste and ore haulage is performed with a fleet of 300 tonne primary haulers. In 2016, we purchased three used 300 tonne haul trucks for the Marigold mine, one of which replaced a rental unit, thereby expanding the haul truck fleet to 21-300 tonne haul trucks. In February 2018, we approved the purchase of four additional 300 tonne class haul trucks for expected service in the third quarter of 2018, which will further expand our fleet to 25-300 tonne haul trucks.

With the low grade nature of the Mineral Reserves and Mineral Resources at the Marigold mine, such large, efficient and cost effective machinery must be utilized for mining.

The Marigold processing plant and facilities incorporate industry standard ROM heap leaching, carbon adsorption, carbon desorption and electro-winning circuits to produce a final precious metal (doré) product.

ROM ore is delivered to the leach pad by haulage truck and stacked in 20 foot to 40 foot lifts. Pebble lime, used for pH control, is added to the haulage trucks from a storage silo prior to dumping. Fresh and spent ore are both ripped and cross-ripped. Final solution distribution to the pad is through a series of header and sub-header lines followed by drip tubing on the surface and impact sprinklers on fresh ore side slopes. The overall barren solution application rate to the leach pads is 0.0030 to 0.0035 gpm/ft2.

The Marigold heap leach solution processing facilities consist of two barren, four pregnant, and one storm water/overflow solution pond. Ancillary facilities include solution pumps and piping, two separate sodium cyanide addition facilities, one sodium hydroxide addition system (barren solution pH adjustment) and three locations for anti-scalant addition.

The heap leach pad has expanded into 18 separate cells (with an additional cell permitted). Barren leach solution (cyanide bearing solution, very low in gold grade) is applied selective y to different areas of the pads. Approximately 4.3 million square feet of pad area is being leached at any given time. Currently, Cells 1, 2, 7, and 8 of the pad are inactive and in drain down phase. The remaining cells are active, except for Cell 19 which is not yet constructed. The barren leach solution is pumped to the leach pad by two independent barren solution distribution systems and one lean solution pumping system. A lean solution is collected separately from heap outlet pipes carrying low gold grade pregnant solution from older or spent areas of the pad. The lean (low grade solution) solution is then recycled back to the heap leach pad by three vertical turbine pumps, via one of the two barren solution pipes in preference to processing through the carbon columns. Combined barren solution flow capacity from the two pumping systems is 11,000 gpm and the maximum lean solution flow rate is 2,500 gpm, for a total solution flow rate to the leach pad of 13,500 gpm. Sodium cyanide is added to the barren solution streams in two separate locations, while sodium hydroxide is added to the carbon column barren solution.

Pregnant solution (gold bearing) from the leach pad is collected in the pregnant solution pond(s) and pumped to five parallel carbon column trains each with five columns to recover gold from solution. Total pregnant solution flow rate through the columns is 10,000 gpm accomplished with six vertical turbine column feed pumps. Column discharge solution reports to the barren ponds where sodium hydroxide and/or sodium cyanide are added before the solution is recycled back to the leach pad.

Loaded carbon from the carbon columns is transported by a dedicated truck to the process facility where gold is eluted (re-dissolved) from the carbon in one of two strip vessels (one twoton capacity carbon vessel and one three-ton capacity carbon vessel). Stripping solution pH is adjusted to 13 with sodium hydroxide, then heated to 285°F by a boiler and series of heat exchangers. Solution flow rate through the carbon bed is 30 to 40 gpm. Stripping continues until the pregnant solution grade assays below 0.50 oz/t. The precious metal bearing solution is passed through two 150 ft3 electro-winning cells in parallel where the metals are plated out of the solution. A third electro-winning cell is used as a re plating cell to further clean the cathodes used in the two primary cells, as required. Electro winning barren solution is recycled back through the strip vessel until the batch process is complete.

The plated material (sludge) resulting from electro-winning is retorted for mercury removal and drying. After retorting, the sludge is mixed with flux and smelted in a propane-fired furnace for final precious metal recovery. Stripped carbon is screened for fine carbon removal, acid washed to remove carbonate scale and thermally reactivated to remove any organic contamination as required prior to return to service at the carbon columns. The entire adsorption/desorption/ recovery (“ADR”) process described above is typical in the industry for treating solutions containing gold cyanide.