Elephant Mountain

Prospect, Active

Commodities and mineralogy

Main commodities Au
Other commodities As; Bi; Mo; Sb
Ore minerals arsenopyrite; bismuth; gold; molybdenite; stibnite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale TN
Quadrangle map, 1:63,360-scale B-1
Latitude 65.2742
Longitude -150.0279
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Elephant Mountain lode prospect is at an elevation of about 3,500 feet on Elephant Mountain at the head of Aloha Creek. It is just east of the center of section 9, T. 5 N., R. 12 W., of the Fairbanks Meridian. The site is the location of drilling from 1999 to 2001. The location is accurate within 1000 feet.

Geologic setting

Geologic description

Elephant Mountain is underlain by a Cretaceous pluton that intrudes Jurassic or Cretaceous quartzite, sandstone, siltstone, and shale (Chapman and others, 1982; Reifenstuhl and others, 1997). The pluton is one of several 90 Ma alkalic plutons in the eastern Tanana, central Livengood, and western Circle quadrangles. Contacts of the Elephant Mountain pluton indicate that it is a northeast-trending, dike-like body about a mile wide and 5 miles long, cut off by high-angle faults at the northeastern and southwestern ends (Reifenstuhl and others, 1997). Its composition ranges from diorite to granite, but it mostly is trachytoidal, quartz-free syenite and subequigranular quartz syenite. The pluton is zoned, and has a core of altered, equigranular quartz syenite, granite, and granite pegmatite (Reifenstuhl and others, 1997).
Soil sampling completed by Placer Dome, Inc. defined an open-ended linear zone of gold and arsenic geochemical anomalies that extends for over 6,000 feet and is up to 1,500 feet wide. Gold contents in soil samples ranged up to 1,540 parts per billion (ppb) (North Star Exploration, Inc., 2000). The mineralized zone is structurally controlled, with prominent northeast- and northwest-trending, and weaker north-trending, patterns. Soil sampling completed by North Star Exploration, Inc., in 1999 indicated that the anomalous zone continues northeast for at least another 2,000 feet (North Star Exploration, Inc., 2000).
Observations from drill holes indicate that higher gold values are associated with fractured and crushed zones, which often become stockwork in nature (North Star Exploration, Inc., 2000). Visible gold also occurs in drill core. Gold is primarily associated with pervasive silicification and quartz veinlets. Arsenopyrite, molybdenite, and stibnite occur in the silicified zones, and there is a strong gold-arsenic correlation. Gold is associated in some drill holes with bismuth (North Star Exploration, Inc., 2000).
The results from a helicopter-borne magnetic-electromagnetic-radiometric survey show that the Elephant Mountain pluton is a nearly featureless, low-magnetic plateau that has coincident high resistivity. Resistivity data at higher frequencies show lineaments that are inferred by North Star to be the effects of surface weathering of fault and fracture zones in the pluton. Some of the soil geochemical anomalies coincide with these lineaments (North Star Exploration, Inc., 2000).
In 2016, Endurance Gold Corporation drill-tested soil anomalies with greater than 100 ppb gold; three holes were drilled in the South Zone and one hole in the North Zone, for a total of 598 m. The South Zone is associated with 1-kilometer-long by 0.25-kilometer-wide gold-arsenic-antimony soil anomaly. The North Zone is associated with a 1-square-kilometer surface-alteration zone with disseminated pyrite and arsenopyrite in a pervasively silica, sericite, clay altered granodiorite and a gold-arsenic soil anomaly. Endurance Gold Corporation’s follow-up plans for 2017 include ground-based geophysical surveys, geochemical sampling, and drilling (Athey and Werdon, 2017).
Geologic map unit (-150.030403565949, 65.2737582801621)
Mineral deposit model Alaskan plutonic-related gold deposit (McCoy and others, 1997).
Age of mineralization Cretaceous, assumed to be contemporaneous with the 89 +/- 1 Ma age of the Elephant Mountain pluton (Reifenstuhl and others, 1997).
Alteration of deposit Pervasive silicification (North Star Exploration, Inc., 2000).

Production and reserves

Workings or exploration
Placer Dome, Inc. discovered visible gold in an outcrop of altered granite on Elephant Mountain in 1991 (North Star Exploration, Inc., 2000). Their soil sampling defined an open-ended linear zone of gold and arsenic geochemical anomalies that extends for over 6,000 feet and is up to 1,500 feet wide. Gold contents in soil samples ranged up to 1,540 parts per billion (ppb) (North Star Exploration, Inc., 2000). Soil sampling by North Star Exploration, Inc. in 1999 indicated that the anomalous zone continues northeast for at least another 2,000 feet (North Star Exploration, Inc., 2000).
Placer Dome, Inc. conducted ground geophysical surveys over portions of Elephant Mountain after a gold-sulfide association was identified while logging drill core (North Star Exploration, Inc., 2000). Their geophysical surveys included magnetics, very low frequency (VLF) gradient induced polarization (IP), resistivity, and limited dipole-dipole IP. A large chargeable zone (1,500 feet wide and 4,500 feet long) was detected between the drilled areas, which Placer Dome, Inc.'s geophysicists attributed to a large volume of material containing a relatively low concentration of sulfides with a small increase in sulfide content at depth.
In 1992, Placer Dome, Inc. dug 6,000 feet of trenches and diamond drilled 10 diamond core holes totaling 4,000 feet (Swainbank and others, 1993). The drill logs indicate that higher gold values are associated with fractured and crushed zones, which often become stockwork in nature (North Star Exploration, Inc., 2000).
Visible gold also occurs in the drill core. Gold is primarily associated with pervasive silicification and quartz veinlets. Arsenopyrite, molybdenite, and stibnite occur in the silicified zones, and there is a strong gold-arsenic correlation. Gold is associated in some drill holes with bismuth (North Star Exploration, Inc., 2000). Placer Dome, Inc.'s best hole was DDH-2, grading an average of 0.015 ounce per ton (oz/t) gold over 326 feet that bottomed in mineralization. Other drill results include 334 feet grading 0.010 oz/t gold in hole DDH-8, 340 feet grading 0.008 oz/t gold in hole DDH-1, and 225 feet grading 0.005 oz/t gold in hole DDH-4 (North Star Exploration, Inc., 2000). The highest drill core sample contained 1,740 ppb gold and several thousand parts per million (ppm) arsenic (Harry Noyes, oral communication, 1996).
A rock sample of altered granite (sample number 96RN185) collected in 1996 by the Alaska Division of Geological and Geophysical Surveys contained 164 ppb gold, 2211 ppm arsenic, and 61 ppm antimony (Liss and others, 1997). Aeromagnetic surveys of the area completed by the Alaska Division of Geological and Geophysical Surveys indicate that the plutonic rocks have fairly low magnetic signatures, whereas the surrounding rocks are more variable (Staff and others, 1997).
North Star Exploration, Inc. conducted a helicopter-borne, magnetic-electromagnetic-radiometric survey over Elephant Mountain (North Star Exploration, Inc., 2000). The results show that the Elephant Mountain pluton is a nearly featureless, low-magnetic plateau that has coincident high resistivity. Resistivity data at higher frequencies show lineaments that are inferred by North Star Exploration, Inc. to be the effects of surface weathering of fault and fracture zones in the pluton. Some of the soil geochemical anomalies coincide with these lineaments. In 2000, North Star Exploration, Inc. drilled two core holes totaling 631 feet at Elephant Mountain and encountered arsenopyrite with geochemically anomalous gold in silicified granite (North Star Exploration, Inc., 2001; Szumigala and others, 2001).
A 2007 prospecting and sampling program resulted in the discovery of gold values in grab samples of quartz vein material from the intrusive including 12.98 grams per tonne (g/t), 5.21 g/t, 3.02 g/t, 2.59 g/t and 2.18 g/t gold. These high gold values were collected where Placer Dome, Inc. collected a grab sample in 1991 that assayed 12 oz/t gold (411.4 g/t gold). This quartz vein is approximately one kilometer south of the best Placer Dome, Inc. drill hole and is defined by a greater than 100 ppb gold-in-soil anomaly within a 150 by 800 meter area (Endurance Gold Corporation, 2015b).
In 2013 Endurance Gold Corporation completed a reconnaissance prospecting rock and soil sampling program collecting 61 rock grab samples with the best gold values associated with altered intrusive and quartz vein stock-work material including 4,440 ppb gold, as well as 1920 ppb, and 1880 ppb gold (Endurance Gold Corporation, 2014). In 2014 Endurance Gold Corporation completed an orientation survey of 36 power-assisted auger soil samples at recovery depths of between 0.81 and 1.52 meters. These deep soil samples, with peak values up to 320 ppb gold at 1.52 meters (5 feet) depth, together with shallower soil samples collected in 2013, have confirmed a strong and continuous 600 meter long soil anomaly which exceeds 100 ppb gold (Endurance Gold Corporation, 2015a).
In 2016, Endurance Gold Corporation drill-tested soil anomalies with greater than 100 ppb gold; three holes were drilled in the South Zone and one hole in the North Zone, for a total of 598 m. Highlights of South Zone drilling include 4.09 grams of gold per tonne over 4.6 m, including 20.4 grams of gold per tonne over 0.67 meter spatially associated with 1-kilometer-long by 0.25-kilometer-wide gold-arsenic-antimony soil anomaly. Highlights of North Zone drilling include 0.40 gram of gold per tonne over 147.1 m, including 0.63 gram of gold per tonne over 48.2 meters spatially associated with a 1-square-kilometer surface-alteration zone with disseminated pyrite and arsenopyrite in a pervasively silica, sericite, clay altered granodiorite and a gold-arsenic soil anomaly. Endurance Gold Corporation’s follow-up plans for 2017 include ground-based geophysical surveys, geochemical sampling, and drilling (Athey and Werdon, 2017).
Indication of production None

References

References

North Star Exploration, Inc., 2000, Elephant Mountain intrusion-hosted gold prospect: unpublished company brochure, 4 p., 2 small-scale maps, 1 cross-section.
North Star Exploration, Inc., 2001, Alaska exploration opportunities: unpublished company brochure, 4 p.
Reporters D.J. Szumigala (ADGGS); N.V. King (Alaska Earth Sciences); M.B. Werdon (DGGS)
Last report date 8/26/2017