Elephant Mountain Prospects, Rampart Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Elephant Mountain Prospects	Group of Prospects
Rampart Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

Location: 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 in 1999-2001 on a claim block consisting of 140 state mining claims and 7 prospecting sites that stretched from the junction of Aloha and Minook creeks on the west, to the headwaters of Chapman Creek on the north, and into the Livengood quadrangle on the east. This claim block, called the Orion claims, covers the southwest half of a broad, flat-topped ridge system that includes Elephant Mountain. The location is accurate within 1000 feet.
Geology: 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 [RI 97-15a]). 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, dikelike 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 [RI 97-15a]). 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 [RI 97-15a]). Placer Dome, Inc., discovered visible gold in an outcrop of altered granite on Elephant Mountain in 1991 (North Star Exploration, Inc., 2000 [Elephant Mountain intrusion-hosted gold prospect]). 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 [Elephant Mountain intrusion-hosted gold prospect]. The mineralized zone is structurally controlled, with prominent northeast- and northwest-trending, and weaker north-trending, patterns. 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 [Elephant Mountain intrusion-hosted gold prospect]). 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). Samples of quartz veins collected by industry contained up to 12.2 ounces of gold per ton (North Star Exploration, Inc., 2000 [Elephant Mountain intrusion-hosted gold prospect]), and analyses of drill core showed values of up to 1,740 ppb gold and several thousand parts per million (ppm) arsenic (Harry Noyes, oral commun., 1996). Aeromagnetic surveys of the area 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 [Elephant Mountain intrusion-hosted gold prospect]). 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 linears that are inferred by North Star to be the effects of surface weathering of fault/fracture zones in the pluton. Some of the soil geochemical anomalies coincide with these linears. Placer Dome 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 [Elephant Mountain intrusion-hosted gold prospect]). Their geophysical surveys included magnetics, 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'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 [Elephant Mountain intrusion-hosted gold prospect]). 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 [Elephant Mountain intrusion-hosted gold prospect]). Placer Dome's best hole was DDH-2, grading an average of 0.015 ounce of gold per ton over 326 feet that bottomed in mineralization. Other drill results include 334 feet grading 0.010 ounce of gold per ton in hole DDH-8, 340 feet grading 0.008 ounce of gold per ton in hole DDH-1, and 225 feet grading 0.005 ounce of gold per ton in hole DDH-4 (North Star Exploration, Inc., 2000 [Elephant Mountain intrusion-hosted gold prospect]). 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 [Alaska exploration opportunities]; Szumigala and others, 2001). The drilling area is in a broad, flat swale along the main ridgeline at 3,300 feet elevation.
Workings: Placer Dome, Inc., discovered visible gold in an outcrop of altered granite on Elephant Mountain in 1991 (North Star Exploration, Inc., 2000 [Elephant Mountain intrusion-hosted gold prospect]). 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 [Elephant Mountain intrusion-hosted gold prospect]. The mineralized zone is structurally controlled, with prominent northeast- and northwest-trending, and weaker north-trending, patterns. 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 [Elephant Mountain intrusion-hosted gold prospect]). 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). Samples of quartz veins collected by industry contained up to 12.2 ounces of gold per ton (North Star Exploration, Inc., 2000 [Elephant Mountain intrusion-hosted gold prospect]), and analyses of drill core showed values of up to 1,740 ppb gold and several thousand parts per million (ppm) arsenic (Harry Noyes, oral commun., 1996). Aeromagnetic surveys of the area 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 [Elephant Mountain intrusion-hosted gold prospect]). 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 linears that are inferred by North Star to be the effects of surface weathering of fault/fracture zones in the pluton. Some of the soil geochemical anomalies coincide with these linears. Placer Dome 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 [Elephant Mountain intrusion-hosted gold prospect]). Their geophysical surveys included magnetics, 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'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 [Elephant Mountain intrusion-hosted gold prospect]). 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 [Elephant Mountain intrusion-hosted gold prospect]). Placer Dome's best hole was DDH-2, grading an average of 0.015 ounce of gold per ton over 326 feet that bottomed in mineralization. Other drill results include 334 feet grading 0.010 ounce of gold per ton in hole DDH-8, 340 feet grading 0.008 ounce of gold per ton in hole DDH-1, and 225 feet grading 0.005 ounce of gold per ton in hole DDH-4 (North Star Exploration, Inc., 2000 [Elephant Mountain intrusion-hosted gold prospect]). 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 [Alaska exploration opportunities]; Szumigala and others, 2001).
Age: Cretaceous, assumed to be contemporaneous with the 89 +/- 1 Ma age of the Elephant Mountain pluton (Reifenstuhl and others, 1997 [RI 97-15a]).
Alteration: Silicification.

Commodities (Major) - Au; (Minor) - As, Bi, Mo, Sb
Development Status: None
Deposit Model: Porphyry Cu-Au (Cox and Singer, 1986; model 20c); Alaskan plutonic-related gold

Other Databases

Link to USGS - Alaska:	TN067

Other Regions, Features and Areas containing this locality

References