Island Mountain

Prospect, Active

Commodities and mineralogy

Main commodities Au; Cu; Mo; Zn
Other commodities Ag; As; Fe
Ore minerals arsenopyrite; chalcopyrite; gold; magnetite; molybdenite; pyrite; pyrrhotite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale TY
Quadrangle map, 1:63,360-scale D-8
Latitude 61.7748
Longitude -152.7594
Nearby scientific data Find additional scientific data near this location
Location and accuracy The center of the Island Mountain prospect is about 3.2 miles south-southwest of the mouth of Emerald Creek on the Skwentna River. It is about 0.5 mile west of the center of section 33, T. 20 N., R. 19 W., of the Seward Meridian. The prospect occupies much of the prominent mountain between Emerald Creek and the Skwentna River. The location is accurate to within 500 feet.

Geologic setting

Geologic description

The rocks in the area are Jurassic and Cretaceous sediments of the Kahlitna terrane that are intruded by a small body of Cretaceous or Tertiary granite and quartz monzonite (Reed and Elliott, 1970; Wilson and others, 2009). As studied by Cominco American (unpublished reports, 1987 and 1988), the Island Mountain deposit consists of pyrite-chalcopyrite-quartz veins; disseminated pyrite and chalcopyrite; and arsenopyrite-gold and stockwork quartz veins with magnetite and trace molybdenite. The mineralization is in fine- to medium- grained plagioclase-hornblende porphyritic andesite and medium-grained monzonite that are probably related to the mineralization. Carbonate-rich beds in the sedimentary country rocks are locally replaced with pyrrhotite, pyrite, and sphalerite.
As mapped by Kiska Metals (2010b), the Island Mountain prospect covers an area about 3 by 4 kilometers in size. Monzonite porphyry, diorite, and monzonite intrude argillite and hornfels at the prospect. Kiska Metals drilled two holes in 2006 and two holes in 2009. The first hole in 2009 targeted a hydrothermal breccia zone 150 meters in diameter. Surface samples from the breccia zone contained actinolite, magnetite, pyrrhotite, pyrite, and chalcopyrite, and assayed up to 1.19 gram of gold per tonne, 5.2 grams of silver per tonne, and 0.2 percent copper. The hole intersected two zones of gold mineralization. A 150-meter intercept averaged 0.72 gram of gold per tonne; a 106.9 intercept averaged 1.22 grams of gold per tonne. The hole was almost entirely in diorite. The second hole averaged 0.13 gram of gold per tonne over 202.3 meters. Kiska Metals considers the deposit to be a gold-copper porphyry similar to the Whistler deposit (TY022) to the north.
The Island Mountain area has extensive gold-copper soil geochemical anomalies and significant porphyry-related mineralization, alteration and brecciation. Porphyry centers, as defined by central zones of potassic alteration associated with gold-copper mineralization and airborne magnetic high anomalies have been confirmed at four zones: the Breccia Zone, Cirque Zone, Howell Zone and Gilligan Zone. In addition, the Super Conductor is a 1 kilometer by 1.8 kilometers area defined by a strong airborne EM conductor associated with disseminated pyrrhotite and local gold mineralization (Roberts, 2014).
Roberts (2014) describes mineralization as gold-copper porphyry mineralization typical of the 'reduced'-type porphyry systems where pyrrhotite is a dominant sulfide (e.g. Catface deposit, BC). Gold-copper porphyry mineralization has been intersected in drilling at two separate centers at Island Mountain (Breccia Zone and Cirque Zone). In contrast to the Whistler porphyry systems, which are 22 kilometers south, Island Mountain has significantly different alteration, veining, brecciation and sulfide assemblages associated with mineralization, principally the occurrence of pyrrhotite associated with gold-copper mineralization, core zones of mineralization hosted by magmatic-hydrothermal breccias, strong sodic-calcic alteration, lack of significant sulfates, very minor hydrothermal quartz and weak to insignificant phyllic alteration. For these reasons, the porphyry systems at Island Mountain may belong to the 'reduced' subclass of porphyry copper-gold deposits. In addition to these known occurrences, there are multiple zones with similar features (e.g. Howell Zone, Super Conductor). At the southern end of the Breccia Zone, the Discovery Breccia is comprised of intermingled intrusive and hydrothermal matrix breccias dominated by sodic-calcic alteration. This breccia complex records early pervasive biotite alteration, local k-feldspar alteration with disseminated followed by strong actinolite-albite alteration. Assays returned several significant intercepts of predominantly gold mineralization including a deep, strongly silicic/possibly potassic zone containing massive pyrite-dominant sulfide veins (IM11-030), a style not seen previously at Island Mountain (Roberts, 2014).
One target outside of the Breccia Zone at Island Mountain is the Howell Zone, which occurs 2 kilometers to the northeast. The Howell Zone is defined by very strong gold, copper, and molybdenum soil anomalies over significant widths. In addition, a 2011 airborne electro-magnetic (EM) survey identified a significant 1800 meters by 1000 meters conductor to the east of the Breccia Zone, which is largely hidden by colluvial and alluvial cover. This EM anomaly is interpreted to potentially represent a large zone of disseminated or net-textured pyrrhotite, which may be similar to the pyrrhotite-gold zone located east of the Discovery Breccia (Roberts, 2014).
Geologic map unit (-152.761606571811, 61.7742074296708)
Mineral deposit model Gold-copper porphyry (Cox and Singer, 1986; model 20c)
Mineral deposit model number 20c
Age of mineralization Younger than, or genetically related to the Late Cretaceous diorite to monzonite dikes, sills, and stocks, referred to as the Whistler Intrusive Suite with an Ar-Ar hornblende age date for 75 +/- 0.3 million years (Morris, 2011).
Alteration of deposit In contrast to the Whistler porphyry systems, which are 22 kilometers south, Island Mountain has significantly different alteration, veining, brecciation and sulfide assemblages associated with mineralization, principally the occurrence of pyrrhotite associated with gold-copper mineralization, core zones of mineralization hosted by magmatic-hydrothermal breccias, strong sodic-calcic alteration, lack of significant sulfates, very minor hydrothermal quartz and weak to insignificant phyllic alteration. For these reasons, the porphyry systems at Island Mountain may belong to the 'reduced' subclass of porphyry copper-gold deposits. In addition to these known occurrences, there are multiple prospects with similar features (e.g. Howell Zone, Super Conductor). At the southern end of the Breccia Zone, the Discovery Breccia is comprised of intermingled intrusive and hydrothermal matrix breccias dominated by sodic-calcic alteration. This breccia complex records early pervasive biotite alteration, local k-feldspar alteration with disseminated followed by strong actinolite-albite alteration (Roberts, 2014).

Production and reserves

Workings or exploration
The Island Mountain area was discovered by Cominco Alaska, who worked in the area from 1986 to 1989 (Wahl and others, 2008). Kennecott Exploration Company was active in the area from 2004 to 2006 and staked a large block of claims that covered the Island Mountain prospect. Geoinformatics Exploration Inc. acquired the property from Kennecott in 2007 and in 2009, Kiska Metals Corporation was formed by a merger of Geoinformatics and Rimfire Minerals Corporation. In early 2010, Kiska Metals (2010a) was exploring their claim blocks as the Whistler project and they drilled the Island Mountain prospect in 2009.
Historic exploration included silt sampling, mapping, rock and contour soil sampling, soil grid geochemical surveys, magnetic and VLF geophysical surveys and diamond drilling by Cominco America in the mid-1980s. Similar work continued to 2009 by Kennecott and Kiska Metals. Kiska Metals drilled two holes in 2006 and 2 holes in 2009 (Kiska Metals Corporation, 2009).
During the 2009 to 2010 field seasons, Kiska completed 8,660 meters of diamond drilling in 23 drill holes, 224 line-kilometers of 3D induced polarization (IP) geophysics, 40 line-kilometers of 2D IP geophysics, geological mapping, geochemical sampling and metallurgical testing of mineralization from the Breccia Zone at Island Mountain (Roberts, 2014).
Kiska continued to drill and explore Island Mountain for the duration of the 2010 and 2011 field seasons, including step-out drilling at the Island Mountain Breccia Zone, an airborne EM survey of the Island Mountain area (Roberts, 2014).
The Island Mountain area has extensive gold-copper soil geochemical anomalies and significant porphyry-related mineralization, alteration and brecciation. Porphyry centers, as defined by central zones of potassic alteration associated with gold-copper mineralization and airborne magnetic high anomalies have been confirmed at four zones: the Breccia Zone, Cirque Zone, Howell Zone and Gilligan Zone. In addition, the Super Conductor is a 1 kilometer by 1.8 kilometers area defined by a strong airborne EM conductor associated with disseminated pyrrhotite and local gold mineralization (Roberts, 2014).
Kiska drilled the first drill hole in the Breccia Zone in 2009 (IM09-001), in which 150 meters averaged 0.72 gram of gold per tonne and 0.16 percent copper primarily in actinolite-magnetite breccia, and 106.9 meters averaged 1.22 grams of gold per tonne and 0.05 percent copper in a deeper pyrrhotite-gold zone. Kiska has conducted a total of 15,572 meters of exploration drilling at Island Mountain from 40 diamond drill holes, with the majority of those holes targeting the Breccia Zone (34 drill holes). At the southern end of the Breccia Zone, the Discovery Breccia is comprised of intermingled intrusive and hydrothermal matrix breccias dominated by sodic-calcic alteration. Assays returned several significant intercepts of predominantly gold mineralization including a deep, strongly silicic/possibly potassic zone containing massive pyrite-dominant sulfide veins (IM11-030), a style not seen previously at Island Mountain. This zone returned 73.9 meters averaging 0.72 gram of gold per tonne, 2.24 grams of silver per tonne and 0.09 percent copper (Roberts, 2014).
One target outside of the Breccia Zone at Island Mountain is the Howell Zone, which occurs 2 kilometers to the northeast. The Howell Zone is defined by very strong gold, copper, and molybdenum soil anomalies over significant widths. The core of the zone is defined by a semicircular 650 meters diameter zone with greater than 90th percentile gold-in-soil values (greater than 0.362 part per million (ppm) gold) with coincident greater than 90th percentile copper (greater than 498 ppm copper) and molybdenum (greater than 17 ppm molybdenum) soil anomalies extending a further 250 meters to the southwest. The core of this anomaly is coincident with a very strong, sub-circular magnetic high anomaly (Roberts, 2014).
In addition, a 2011 airborne electro-magnetic (EM) survey identified a significant 1800 meters by 1000 meters conductor to the east of the Breccia Zone, which is largely hidden by colluvial and alluvial cover. This EM anomaly is interpreted to potentially represent a large zone of disseminated or net-textured pyrrhotite, which may be similar to the pyrrhotite-gold zone located east of the Discovery Breccia. Kiska subsequently tested this anomaly with three widely spaced diamond drill holes for a total of 602 meters. Only one of these holes adequately tested this anomaly, and returned two gold-bearing intervals associated with net-textured pyrrhotite that averaged 0.61 gram of gold per tonne equivalent over 21 meters and another averaging 0.45 gram of gold per tonne equivalent over 30.0 meters (Roberts, 2014).
Indication of production None
Reserve estimates
In 2016, Brazil Resources Inc. (now Gold Mining Inc.) is evaluating prospects it acquired from Kiska Metals Corporation in 2015. Although no on-site work was performed in 2016 at the Whistler (TY022), Raintree West (TY038), and Island Mountain porphyry copper–gold–silver prospects, in May of 2016, Brazil Resources Inc. released a new technical report announcing the first resource estimates for the Raintree West (TY038) and Island Mountain deposits, largely based on drilling by Kiska Metals Corporation between 2009 and 2011 (Giroux, 2016; Athey and Werdon, 2017).
The Island Mountain deposit contains an indicated resource of 31.08 million tonnes averaging 0.49 gram of gold per tonne (490,000 ounces of gold), 1.10 grams of silver per tonne (1.1 million ounces of silver), and 0.06 percent copper (41.12 million pounds of copper). Additionally, Island Mountain contains an inferred resource of 82.02 million tonnes averaging 0.47 gram of gold per tonne (1.24 million ounces of gold), 1.02 grams of silver per tonne (2.69 million ounces of silver), and 0.05 percent copper (90.43 million pounds of copper). The resource is based on 12,668 meters of drilling in 34 holes on the southwest slope of Island Mountain and a cut-off grade of 0.3 gram gold equivalent per tonne (Giroux, 2016).
Production notes None.

Additional comments

The 2009 to 2010 field program was operated by Kiska under the direction of a Technical Committee comprised of two Kennecott and two Kiska employees. In August of 2010, Kiska delivered a Technical Report to Kennecott summarizing the results of the completed 'Trigger Program'. In September of 2010, Kennecott informed Kiska that it would not exercise its back-in right on the project and hence retained a 2 percent Net Smelter Royalty on the property (Kiska Metals Corporation, 2010a).

References

MRDS Number A106267

References

Kiska Metals Corporation, 2009, Kiska drills 106.9 metres of 1.22 g/t gold at Island Mountain area, Whistler, Alaska: (News release, November 2, 2009) http://www.kiskametals.com/s/News.asp?ReportID=369977 (as of January 7, 2015).
Kiska Metals Corporation, 2010a, Whistler project overview; http://www.kiskametals.com/s/Whistler.asp?ReportID=370036 (as of February 26, 2010).
Kiska Metals Corporation, 2010b, Maps and figures: http://www.kiskametals.com/s/Whistler.asp?ReportID=370037 (as of February 28, 2010).
Morris, R.J., 2011, Resource Estimate Update for the Whistler Gold Copper Deposit and Results of Property Wide Exploration, Yentna Mining District, Alaska: Technical Report (43-101) for Kiska Metals Corporation, 133 p. (posted on www.sedar.com, March 18, 2011) http://www.sedar.com/GetFile.do?lang=EN&docClass=24&issuerNo=00007774&fileName=/csfsprod/data115/filings/01703222/00000003/i%3A%5CSEDAR%5CKMTchRpAM.PDF (as of January 8, 2015).
Roberts, Michael, 2014, Whistler Project Executive Summary Report, Kiska Metals Corporation: http://www.kiskametals.com/i/pdf/Kiska_Whistler_ExecutiveSummary_24Jan2014.pdf (as of March 10, 2014).
Wahl, George, Coutture, Jean-Francois, and Keller, G.D., 2008, Mineral resource estimation, Whistler copper-gold project, Alaska Range, Alaska: Technical report for Geoinformatics Exploration, Inc., 124 p. (posted on www.sedar.com, February 22, 2008) http://www.sedar.com/GetFile.do?lang=EN&docClass=24&issuerNo=00007774&fileName=/csfsprod/data86/filings/01219440/00000001/s%3A%5Cgxl222.pdf (as of January 8, 2015).
Reporters Madelyn A. Millholland (Anchorage); D.J. Grybeck (Contractor, U.S. Geological Survey); V.C. Zinno (Alaska Earth Sciences, Inc.); M.B. Werdon (DGGS)
Last report date 8/26/2017