Indian RiverTrend; IRT; IR Prospects, Hughes Mining District, Yukon-Koyukuk Census Area, Alaska, USAi

Regional Level Types
Indian RiverTrend; IRT; IR Prospects	Group of Prospects
Hughes Mining District	Mining District
Yukon-Koyukuk Census Area	Census Area
Alaska	State
USA	Country

This site is the Indian River trend, U.S. BLM MILS location 0020470019 (Oddenino and others, 1995; Interagency Minerals Coordinating Group, 2004).
Location: This site represents several prospects in a linear, east-northeast-trending belt, informally called the Indian River trend, on the southeastern side of the Indian Mountains. The belt is marked by a well-defined color anomaly 8 miles long and a half-mile wide. The easternmost prospect is approximately 2 miles south of the Utopia Creek placer mine (MZ006). The site is centered on an area of drill holes in the northwest corner of section 8, T. 6 N., R. 24 E., Kateel River Meridian (State of Alaska Department of Natural Resources, 2000). The location is accurate within 1,000 feet.
Geology: The mineralization along the Indian River trend is in Lower Cretaceous andesitic volcanic rocks (Patton and others, 1977). The andesite is interbedded with pillow basalt, andesitic tuff, volcanic conglomerate, volcanic breccia, chert, cherty tuff, and coquinoidal limestone. An east-west, high-angle fault cuts the rocks, and small bodies of Cretaceous dacite and rhyolite porphyry intrude along the fault. The dacite and rhyolite intrusive rocks are intensely silicified and contain disseminated pyrite (Miller and Ferrians, 1968). Oxidation of the pyrite resulted in the formation of conspicuous orange, red, and yellow gossans; about 10 color anomalies developed as a result of this oxidization occur along 6 miles of the fault (Kurtak and others, 2002). Semi-quantitative analyses of samples of typical altered, intrusive rock showed small but anomalous amounts of lead, copper, silver, and gold (Miller and Ferrians, 1968). The highest values for 5 samples of altered, pyritiferous, andesite and oxidized, pyritiferous dacite were 0.1 part per million (ppm) gold, 7 ppm silver, 300 ppm copper, and 300 ppm lead. Stream-sediment samples in the area contained 30 to 50 ppm copper and up to 20 ppm lead. The Alaska Division of Geological & Geophysical Surveys collected 3 rock samples at 2 localities along the west side of Macaroni Creek (Liss and others, 1993). The samples included latite porphyry, leached porphyry, and andesite containing magnetite and sulfides. The sample of andesite with magnetite and sulfides contained 7 parts per billion (ppb) gold, 47 ppm arsenic, and 25 ppm antimony. North Star Exploration, Inc. conducted exploration in the late 1990s across the Indian River trend area as part of a mineral evaluation of Doyon Limited's lands (North Star Exploration, Inc., 2000). The andesite and dacite in the prospect area have been moderately to intensely altered, mainly by argillization, sericitization, and silicification (North Star Exploration, Inc., 1999 [Mineral potential of the Hughes Block Interior Alaska]). Crosscutting, high-angle faults appear to offset mineralization at the IRT prospect and may be responsible for localizing alteration. Locally, the rocks consist of quartz-sericite-altered material cut by quartz-stockwork veins, faults and hydrothermal breccias, and pods of intense silicification. Outward from a core of silicification, clay- and propylitically-altered rocks are developed. Pyrite occurs locally in quartz as fine-grained disseminations and small spheroids. Veins of anhydrite and barite are also present. North Star's samples of altered andesite in the Indian River trend contained locally anomalous gold values (North Star Exploration Inc., 2000). Their soil grids and other samples at the IRT prospect showed areas of mineralization up to 1,200 feet by 1,200 feet in area that contain up to 380 ppb gold, and anomalous values of arsenic and barite. Samples from several trenches on the prospect contained up to 327 ppb gold along 10 feet. The gold to silver ratios in samples from two of the soil grids, the My and Sili, are higher than grids elsewhere on the IRT property. North Star drilled 2 diamond core holes totaling 1,091 feet on the Indian River trend during 2000 (North Star Exploration, Inc., 2001). Samples of the core showed anomalous gold, silver, copper, lead, and zinc (North Star Exploration, Inc., 2001). Chalcopyrite and pyrite occur throughout much of the core and gypsum is present as an alteration product (Szumigala and others, 2001). North Star also contracted an airborne (helicopter) magnetic, electromagnetic, and radiometric geophysical survey. Geophysical interpretation of the survey suggest that a window exists through the andesite into a unit that consists mainly of sedimentary rocks, and they indicate exploration potential for sediment-hosted as well as volcanic-hosted gold deposits (North Star Exploration, Inc., 2000). The linear trend of the small intrusions may represent a fossil hot springs environment and the IRT prospect may be the uppermost levels of an auriferous epithermal system (North Star Exploration, Inc., 1999 [Mineral potential of the Hughes Block Interior Alaska]). The U.S. Bureau of Land Management sampled 2 sites along the Indian River trend from 1997 to 2000 (Kurtak and others, 2002). Analytical results from a sample of brick-red soil from the My soil grid about 0.2 miles east of Macaroni Creek, contained 91 ppb gold, 9,166 ppm lead, and 517 ppm barium. A sample of altered rhyolite with 5 percent pyrite assayed 36 ppb gold (Klieforth and others, 2001). The Bureau also collected 2 samples of silicified rhyolite with 3 percent pyrite, and 15 soil samples from a backfilled trench and a soil-grid line at the Macaroni prospect, near the north end of a 150-foot by 350-foot color anomaly (Kurtak and others, 2002). Seven of the soil samples had detectable gold values ranging from 6 to 24 ppb gold, but the other samples did not show anomalous metal values.
Workings: The mineralization was first described by Miller and Ferrians (1968); their geochemical analyses of rock samples of typical altered intrusive rock contained small but anomalous amounts of lead, copper, silver, and gold. The highest analytical values for 5 samples of altered, pyritiferous, andesite and oxidized, pyritiferous, dacite were 0.1 part per million (ppm) gold, 7 ppm silver, 300 ppm copper, and 300 ppm lead. Stream-sediment samples in the area contained 30 to 50 ppm copper and up to 20 ppm lead. The Alaska Division of Geological & Geophysical Surveys collected 3 rock samples at 2 localities along the west side of Macaroni Creek (Liss and others, 1993). The samples included latite porphyry, leached porphyry, and andesite with magnetite and sulfides. The sample of andesite with magnetite and sulfides contained 7 parts per billion (ppb) gold, 47 ppm arsenic, and 25 ppm antimony. North Star Exploration, Inc. conducted exploration in the late 1990s across the Indian River trend area as part of a mineral evaluation of Doyon Limited's lands (North Star Exploration, Inc., 2000). The andesite and dacite in the prospect area have been moderately to intensely altered, mainly by argillization, sericitization, and silicification (North Star Exploration, Inc., 1999 [Mineral potential of the Hughes Block Interior Alaska]). Crosscutting, high-angle faults appear to offset mineralization at the IRT prospect and may be responsible for localizing alteration. Locally, the rocks consist of quartz-sericite-altered material cut by quartz-stockwork veins, faults and hydrothermal breccias, and pods of intense silicification. Outward from a core of silicification, clay- and propylitically-altered rocks are developed. Pyrite occurs locally in quartz as fine-grained disseminations and small spheroids. Veins of anhydrite and barite are also present. North Star's samples of altered andesite in the Indian River trend contained locally anomalous gold values (North Star Exploration Inc., 2000). Their soil grids and other samples at the IRT prospect showed areas of mineralization up to 1,200 feet by 1,200 feet in area that contain up to 380 ppb gold, and anomalous values of arsenic and barite. Samples from several trenches on the prospect contained up to 327 ppb gold along 10 feet. The gold to silver ratios in samples from two of the soil grids, the My and Sili, are higher than grids elsewhere on the IRT property. North Star drilled 2 diamond core holes totaling 1,091 feet on the Indian River trend during 2000 (North Star Exploration, Inc., 2001). Samples of the core showed anomalous gold, silver, copper, lead, and zinc (North Star Exploration, Inc., 2001). Chalcopyrite and pyrite occur throughout much of the core and gypsum is present as an alteration product (Szumigala and others, 2001). North Star also contracted an airborne (helicopter) magnetic, electromagnetic, and radiometric geophysical survey. Geophysical interpretation of the survey suggest that a window exists through the andesite into a unit that consists mainly of sedimentary rocks, and they indicate exploration potential for sediment-hosted as well as volcanic-hosted gold deposits (North Star Exploration, Inc., 2000). The linear trend of the small intrusions may represent a fossil hot springs environment and the IRT prospect may be the uppermost levels of an auriferous epithermal system (North Star Exploration, Inc., 1999 [Mineral potential of the Hughes Block Interior Alaska]). The U.S. Bureau of Land Management sampled 2 sites along the Indian River trend from 1997 to 2000 (Kurtak and others, 2002). Analytical results from a sample of brick-red soil from the My soil grid about 0.2 miles east of Macaroni Creek, contained 91 ppb gold, 9,166 ppm lead, and 517 ppm barium. A sample of altered rhyolite with 5 percent pyrite assayed 36 ppb gold (Klieforth and others, 2001). The Bureau also collected 2 samples of silicified rhyolite with 3 percent pyrite, and 15 soil samples from a backfilled trench and a soil-grid line at the Macaroni prospect, near the north end of a 150-foot by 350-foot color anomaly (Kurtak and others, 2002). Seven of the soil samples had detectable gold values ranging from 6 to 24 ppb gold, but the other samples did not show anomalous metal values.
Age: Cretaceous or younger.
Alteration: Argillic, propylitic, sericitic, and silicic alteration.

Commodities (Major) - Ag, Au, Cu, Pb; (Minor) - As, Ba, Sb
Development Status: None
Deposit Model: Hot-spring Au-Ag (Cox and Singer, 1986; model 25a); Comstock epithermal veins (

Other Databases

Link to USGS - Alaska:	MZ004

Other Regions, Features and Areas containing this locality

References