Florida Canyon mine, Imlay Mining District, Pershing County, Nevada, USAi

Regional Level Types
Florida Canyon mine	Mine
Imlay Mining District	Mining District
Pershing County	County
Nevada	State
USA	Country

Sec 2 T31N R33E. Gold mine
Structure: Florida Canyon lies near the intersection of NE-oriented structures of the Midas Lineament and N-S trending Basin and Range normal faults. These deep-seated structures served as conduits for gold-bearing hydrothermal fluids. A strong N30-N50E structural fabric is present in and adjacent to the orebody as evidenced by alignment of quartz veining, shear zones, and well developed joint sets. North-trending anticlines related to Nevadan Orogeny; Basin and Range normal faulting.

Alteration: Silicification, argillization, acid leaching. During Jurassic regional metamorphism, the three primary host lithologies underwent the following changes: 1) in the more siliceous units, quartz was locally recrystallized and feldspar fragments and interstitial clays were mostly converted to sericite, 2) the clay portion of shaley siltstones was altered to sericite while the quartz portion was largely unaffected, and 3) mudstones were converted to argillites consisting mostly of fine grained sericite. Tertiary hydrothermal alteration overprints pervasive metamorphically derived quartz-sericite and is most intense within and adjacent to shear zones and hydrothermal conduits and beneath impermeable rock units. The major hypogene minerals are quartz, kaolinite, and alunite. Quartz occurs as fracture filling, selective replacements of calcareous units, and as irregular flat-lying cryptocrystalline bodies. Hydrothermally altered argillaceous rocks are pervasively kaolinized, although more siliceous units have undergone only minor argillization. Supergene alunite and kaolinite have formed by the downward percolation of acid solutions along faults and fracture zones. These fracture zones often contain calcite, exotic hematite, goethite, and sparse native sulfur. Extensive surficial bleaching is also attributed to acid leaching in the secondary environment. Hematite derived from syngenetic sulfides was mobilized by acid solutions, resulting in a pervasive maroon stain in silty units marginal to bleached areas.

Commodity: Ore Materials: native gold, electrum, kaolinite Gangue Materials: quartz, kaolinite, alunite, pyrite, marcasite, arsenopyrite, hematite, limonite, goethite, opal, calcite, barite, native sulfur, cinnabar, fluorite, manganese oxides, magnetite, adularia.

Deposit: The Florida Canyon epithermal gold deposit is hosted by weakly metamorphosed siltstones and mudstones of the Grass Valley Formation of Triassic age. Gold is hosted in stockwork quartz veins and quartz-sulfide microveinlets which cut the altered Grass Valley Formation. The deposit is localized near the intersection of north-trending Basin and Range faults that bound the west flank of the Humboldt Range and northeast-trending shear zones that may be an expression of the Midas lineament. Late, vertical displacement on the range bounding fault system have juxtaposed the deposit and unaltered basin-fill gravel. To date 76,716,000 tonnes of ore averaging 0.64 g/t (0.019 oz/t) of gold have been produced form the upper, oxidized portion of the deposit.Rocks distal to the orebody that were minimally effected by hydrothermal activity consist primarily of quartz, illite and chlorite. The deposit is associated with pervasive disseminations and fracture fillings of hydrothermal minerals that comprise three mappable zoned alteration types: 1) a central, silicic alteration of quartz-adularia veinlets and silicified rock, 2) an intermediate, argillic alteration of relatively abundant kaolinite-illite, and 3) an outer, hematitic alteration of hematite-goethite that lacks chlorite. The silicic alteration largely follows north- and northeast-trending structures and locally contains pockets of friable quartz, native sulfur, cinnabar, and alunite. Electrum and native gold have been identified in quartz veinlets; gold-silver ore has been mined from all three alteration zones. The ubiquitous presence of auriferous quartz veinlets and silicified rock at the Florida Canyon deposit suggests that the entire exposed section of host rocks was initially affected by hydrothermal reactions below a water table. A subsequent relative drop in the water table, probably related to vertical movements along Basin and Range faults, superimposed the effects of vapor-related alteration on earlier assemblages, including the formation of native sulfur, alunite, cinnabar, and some kaolinite and iron oxides and hydroxides. The mine occurs in Triassic rocks that form the west limb of a complexly faulted anticline. The oldest rocks in the district are felsites and tuffs of the Rochester Rhyolite and rhyolite porphyry intrusive of the Koipato Group. These rocks are overlain by the Prida Formation and locally capped by limestone of the Natchez Pass Formation. Diabase and diorite dikes and sills intrude the Triassic rocks throughout the district. Gold occurs as free gold in quartz veins that also contain subordinate silver, lead, and copper. These veins are typical quartz fissure veins in or near fault zones and also locally occur at contacts with diabasic dikes. MINE WORKINGS HAVE OBLITERATED SEVERAL MINE SHAFTS AND OTHER WORKINGS SHOWN IN THE W/2 SEC. 2 ON THE IMLAY 15-MIN. TOPO MAP. LAND HOLDINGS 3192 HA AS OF 1/91. MINE LIFE 9.5 YR AS OF 1/91. WASTE TO ORE RATIO 1.63:1 AS OF 1/91.

Deposit type: Epithermal vein, Comstock

Development: Prospecting of quartz veins at Florida Canyon dates back at least to the 1870s. In 1925, two cars of kaolin were mined and shipped from the prospect. In 1936 tunnels were driven to explore several silicified outcrops carrying values in gold. In 1969 Homestake Mining Company acquired a lease on claims from the original owner, Samuel N. Moore. Seven wide-spaced rotary holes were drilled, but results were marginal and the lease dropped. The property was next leased by Cordex Exploration Company from 1972-1978. A comprehensive program of geologic mapping, geochemical sampling, trenching, and drilling of 37 holes was completed. 25 of these holes were drilled in the mineralized zone now referred to as the West Trend orebody. The next significant work was done by Flying "J" Mines, which carried out a limited heap leach operation using ore form the West Trend area. In 1980-81, a 69 hole rotary drilling program was performed by ASARCO in the West Trend area and on ground to the south. This work significantly expanded the known mineralization, but due to the low gold grades, ASARCO dropped most of its interest in the property. In 1982, the property was acquired by Montoro Gold Company, a subsidiary of Pegasus Gold Corporation. Detailed geologic mapping and geochemical sampling programs discovered additional gold occurrences throughout the area. By the end of 1985, 241 holes totaling 26,691 m had been completed in the West Trend orebody and adjacent areas. 46 holes were drilled in other exploration areas to the east and south. Large scale column leach tests on various ore types, size fractions and agglomerations were carried out in conjunction with ore delineation. In November 1985, a production decision was made and work began on the processing facilities in May 1986. The first ore was delivered to the leach pad in September and the first gold was poured in November 1986. Since the haul distance is shorter to the leach pad than the waste dump, leaching of low-grade, run-of-mine ore commenced in 1989. 760,000 tons of run-of-mine material containing between 0.008 and 0.014 opt Au were loaded on a portion of the pad and leached. Recoveries approached 50%, resulting in an estimated 4000 additional ounces being produced during the year. The success of leaching run-of-mine material is evident in the mine plan for 1992 in which roughly 4.3 million tons of run-of-mine material will be mined, in addition to 5.1 million tons of primary crushing ore. Pegasus went into bankruptcy in 200?, but the mine continued to be operated by the subsidiary Florida Canyon Gold Mining Company. The current owner of the property is Apollo Gold Corporation. 2003 was a year of mining transition for Florida Canyon. Ore reserves had been depleted in the three historic open pits and mining moved into two newly developed pits, Switchback and Central. Longer ore haulage from the new pits, combined with marginally lower grades, resulted in higher unit costs and lower gold production compared to historical averages.

Geology: The Basin and Range fault system limits the western margins of the deposit. An unknown portion of the western part of the orebody has likely been displaced beyond mining limits by this faulting. Oxidation extends to depths of 100-200 m and locally deeper. Although gold occurs in unoxidized units, all of the mineable ore developed to date is oxidized. Three types of quartz veins are recognized: 1) widespread quartz veins up to 10 cm in width produced by Jurassic regional metamorphism. These veins are discernible from Tertiary epithermal veining by their distinctive milky appearance derived from the abundance of inclusions; 2) stockwork quartz veining. These veins are the most economically important. The density of stockworks depends largely on the fracturing characteristics of the host sediments. The veining appears random but locally invades bedding plane partings as well as following a strong NNE fabric. Milky comb and clear quartz are the predominant vein filling, sometimes overgrown with adularia. Fe-sulfides (now oxidized) occur within veins and are often sparsely disseminated in adjacent wall rock; 3) large, through-going, banded fissure veins which follow the original NNE structural fabric. These veins represent a later hydrothermal episode that overprints the earlier stockwork veining. Although these veins contain sporadic gold mineralization, none is economically important. THERE ARE NO SULFIDES IN THE MATERIAL MINED AT FLORIDA CANYON.

Ore(s): The deposit is localized near the intersection of north-trending Basin and Range faults that bound the west flank of the Humboldt Range and northeast-trending shear zones that may be an expression of the Midas lineament.

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Link to USGS MRDS:	10310409

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