Deposit Type
Mineralization at MLP most closely resembles Carlin-type sediment-hosted gold systems of northern Nevada. The Mother Lode deposit model includes structurally and stratigraphically-controlled disseminated sulphide and oxide mineralization hosted in primarily in Tertiary sedimentary rocks and rhyolite porphyry dikes. Paleozoic sedimentary rocks comprise a smaller volume host in proximity to dikes and the basal Tertiary unconformity. Tertiary volcanic rocks and debris flow breccias are also mineralized at Mother Lode. Alteration types associated with gold mineralization include passive decalcification and illite-pyrite alteration. Unique features of Mother Lode-style mineralization compared to typical Carlin-type deposits include: the association with fluorine, the significant volume of mineralization that is rhyolite porphyry dike-hosted, elevated tellurium and bismuth, and the generally passive, innocuous, very low-silica nature of the mineralization. Carlin-type gold deposits are generally known to form at depths of >2 kilometers, at temperatures between 180-240oC. Mineralization at Mother lode may have formed at depths of 500-1000 meters or less, and at temperatures <240oC (Weiss, 1996).

Mineralization
Mother Lode is characterized as a sediment, intrusive, and locally volcanic-hosted disseminated gold deposit. Mineralization most closely resembles Carlin-type sediment-hosted gold deposits of north-central Nevada. The Mother Lode deposit formed at ~12.7 Ma, which is much younger than the typical ~40 Ma age in north-central Nevada. The nature of mineralization is rather passive and with very low introduction of secondary silica, suggesting it may have formed at a shallower depth and at lower temperature than typical Carlin-type deposits. Mineralization exhibits geochemical associations between Au and As-Sb-Hg-Tl-Te-Bi-F, with very low Ag and base metals. The Mother Lode deposit model consists of structurally and stratigraphically-controlled disseminated gold mineralization hosted primarily in rhyolite porphyry dikes (Tip) and the Sedimentary Rocks of Joshua Hollow (SRJH). Lesser volume hosts include Paleozoic sedimentary rocks (Psd and Psq), Tertiary volcanic rocks (Tlr), and debris flow breccias (Tox). Mineralization in Tip, SRJH and Tlr is mostly sulphide, but may be oxidized depending on depth. Mineralization in Psd, Psq and Tox is mostly oxide. The current interpretation is that oxide mineralization in Tox is detrital, with mineralized rock having been mass-wasted as scarp breccias into the hanging-wall of the FCF. Paleozoic rocks are most commonly mineralized in proximity to dike margins but are also mineralized along subtle non-dikefilled structures and as pseudo-stratiform jasperoid bodies.

The primary structural control feeding mineralization at Mother Lode is a series of north- trending, 50-70o westdipping rhyolite dike-filled structures. Mineralization is both semi-tabular and highly irregular as fluids ascended along dike-filled structures in the underlying Paleozoic rocks, through the Tertiary unconformity, and expanded upward into the Tertiary section. Mineralizing fluids appear to have bled out laterally away from mineralized dikes into favorable permeable lithologies and secondary structures, including the FCF. Deeper drilling has extended the deposit to the west, where it appears that the FCF plays a significant role as a high-grade structural feeder. The potential for additional mineralized dikes in the vicinity of the FCF at depth to the west below current drilling is a highly attractive target.

Rhyolite dikes along the entire Bare Mountain swarm were subjected to high-temperature, sanidine- and biotitestable alteration shortly after emplacement (Weiss, 1996). At Mother Lode, biotite- stable alteration was followed by a lower temperature pervasive illite-smectite-pyrite event that affected both the dikes and surrounding wall rocks. The illite-smectite-pyrite event penetrates well up into the Lithic Ridge Tuff, forming a large sulphidation halo around the gold mineralization. Illite-smectite-pyrite alteration typically exhibits strongly elevated As, Sb and Tl, and may be well-mineralized or only anomalous in gold. The evidence suggests an early relatively barren illite-pyrite event is followed by an overprinting main stage Au-Te sulphidation event.

Trace element geochemistry associated with gold mineralization in drill hole samples includes: As (max 9262 ppm), Sb (max 1429 ppm), Te (max 16 ppm), Tl (max 17 ppm), Hg (max 30 ppm) and Bi (max 25 ppm). The elements with the strongest correlation to gold are tellurium and arsenic. Base metals are very low at Mother Lode. Elevated base metal values are largely associated with basement rocks. Weiss (1996) reports the presence of fluorite veining and a strong association between gold and fluorine at Mother Lode. Fluorine is not included in the multi-element analysis used by Corvus, but fluorite has been identified in the Mother Lode pit. Petrographic studies by Weiss (1996) on sulphide concentrates from drill holes at Mother Lode identified growth zones in pyrite grains exhibiting concentrations of arsenic. Weiss (1996) concluded that the Mother Lode deposit formed at a depth of 500-1000 meters or less, from gold-bearing fluids with temperatures between 200-240oC. High-grade gold appears to be associated with remobilized carbon, particularly in Tjs and Tjvs in the upper portion of the deposit. Remobilized carbon appears to have accumulated in a blanket-like zone above the upper reaches of the rhyolite dikes.

Jasperoid in Paleozoic rocks appears to have both structural and stratigraphic control. Jasperoid intervals in drill holes commonly contain significant Ag values up to 100 ppm. The average Ag/Au ratio from jasperoid samples is 15:1. The average Ag/Au ratio in non-jasperoid Tertiary rock- hosted samples is <0.5:1. Jasperoid mineralization in Paleozoic rocks may be a separate mineralizing event that predates the main Mother Lode gold system. Jasperoid is typically oxidized and yields high cyanide shake leach recoveries.

Rhyolite dikes along the entire Bare Mountain swarm were subjected to a sanidine- and biotite- stable (potassic), high-temperature alteration shortly after emplacement, as evidenced by secondary hypersaline fluids inclusions in quartz phenocrysts (Weiss, 1996). At Mother Lode, rhyolite dikes and surrounding wall rocks were later subjected to lower temperature, pervasive, illite-smectite alteration and associated disseminated pyrite sulphidation as an early event associated with gold mineralization. This alteration in Mother Lode dikes is progressive in intensity, probably due to proximity to open feeder structures. Biotite goes to chlorite and eventually chlorite gets replaced by pyrite. The groundmass and feldspar phenocrysts get replaced by illite-smectite, calcite and adularia.

The proposed mining method is conventional open pit mining. Mineralized material and waste would be drilled and blasted, then loaded into 227-t payload haul trucks with 34 m3 bucket capacity shovels. The loading and haulage fleet would be supported by track dozers, motor graders, and water trucks. Waste would be hauled to the Waste Rock Management Facility (WRMF) located on Corvus controlled lands. Mill sulphide resources would be hauled to the mill stockpile while run-of-mine oxide (ROM) resources would be hauled and placed directly on the heap leach pad.

The proposed mining operation is owner operated equipment.

Overall pit slope angles of 55° were used in the LG runs. Dilution was not accounted for in the optimization for this preliminary design exercise.

The mine production schedule focused on providing the 8,200 tpd of sulphide mill feed. Adjustments to the grade streaming schedule waste forecast were made to smooth the overall mine equipment demand. Approximately 5.1 M tonnes of sulphide material mined and stockpiled at Corvus’s North Bullfrog Project (NBP) were included in the mill feed schedule to balance the mill throughput. Costs for shipping this material from the NBP to the MLP were included in the financial evaluation.

The mining schedule begins in period -1 and continues through period 7. Mill mineralized material would be stockpiled based in the mining periods where the mine output is greater than the 8,200 tpd mill demand. The stockpiles would be depleted during years that the mine output is less than 8,200 tpd of mil feed material. Approximately one year of processing occurs after mining is complete.

The run-of-mine (ROM) sulphide mineralization would be fed to a primary crusher (gyratory). The primary crusher product would be conveyed to a secondary crusher (cone crusher). The crusher product would be screened to remove 19mm (0.75 in; P80 of 0.5 in) product. The screen oversize would be conveyed to a short-head cone crusher, and the product from the crusher would be returned to the screen. The screen undersize would be stockpiled. The fine crushed mineralization would be conveyed from stockpile to the crusher product bin. The mineralization in the bin would be fed to a ball mill, with the discharge pumped to a cyclone pack.

A conceptual process flowsheet was developed for the bio-oxidation milling of the ROM sulphide mineralization followed by cyanidation for gold extraction based on scoping level test work. Oxide mineralization would be processed on a conventional heap leach pad. The biox-mill is projected to recovery 91% of the contained gold in the whole sulphide mineralization and the heap leach pad is projected to recovery 74% of the contained gold in the oxide mineralization.

CONCEPTUAL BIO-OXIDATION MILL PROCESS FLOWSHEET
The thickener underflow would be pumped to a series of rubber-lined bio-oxidation leach tanks. Initially, acid would be added to adjust the eh/pH of the slurry to desired level and mesophilic culture would be added for bio-oxidation of the sulphides.

The bio-oxidized mineralization would be pressure filtered and washed and sent to a repulp tank. The acidic solution would be recycled with any excess solution sent to tails storage facility (TSF). The oxi ........