|Gold nuggets from Julian|
Creek placer found in 1988.
Largest nugget is 1 ounce.
The mapping of old gold and copper mines and searching for gemstones was fascinating. I published more than a thousand books, articles, professional papers, maps and abstracts. Some of the books I wrote on finding gold deposits (Hausel, 1989, 1991, 1997, 2009; Hausel and Hausel, 2011) and some of the gold articles I published led a few prospectors to find treasures. I was the first person to enter several of these mines in decades. I also had considerable experience in volcanic terrains. When I was at the University of Utah and University of New Mexico, Tertiary and Quaternary volcanic rocks were my specialty. And while working at the Geological Survey of Wyoming, I also explored volcanic rocks associated with the giant porphyry copper-silver deposits in the Absaroka Mountains, gold at the Mineral Hill district and in 1981, I had discovered a few dozen gold anomalies in the Rattlesnake Hills greenstone belt. It is rare for a geologist to discover a new mineral deposit, but even rarer for one to find a whole new district!
The Rattlesnake Hills were missed by everyone else, but I found gold at several locations in the district and in different types of deposits (Hausel, 1994, 1995, 1996). I had predicted the district would yield large-tonnage, low-grade gold deposits due to presence of >40 Tertiary alkalic intrusives that erupted through the greenstone terrain and because of the brittle breccias I found adjacent to Sandy Mountain and Oshihan Hill and the stockworks I found south of Oshihan Hill (Hausel and Jones, 1982a, b). Years later, I also mapped the Leucite Hills volcanic field in southwestern Wyoming (Hausel, 2006). So, I took leave from the State and signed up for another consulting job and headed to Alaska in 1988. I had a great time and it worked out so well that I returned in 1989 - I love Alaska and I can understand Sarah Palin's love for this state! But little did we know, we were about to discover one of the largest gold deposits on earth. And we were optimistic - something that is a requirement (but lacking in most) for good exploration geologists!
According to the mining history of Alaska, placer gold had been found in the Kuskokwim River basin in the 1800s. Prospectors worked the George, upper Holitna, Tuluksak, Salmon and Kwethluk rivers; the New York, Bear, California, Marvel, Taylor, Forty-seven, Canyon, Crooked, Julian, Donlin and Flat creeks; and Murray, Snow, Ruby, Quartz, Queen and Lewis gulches. The Nixon Fork mine, 30 miles northeast of the McGrath village, had limited production in 1917 and again in the 1950s. The deposit was a high-grade gold-copper skarn with at least 131,500 ounces of gold (Bluemink, 2009). Eighty miles north of the Nixon Fork, placers in the Ruby district yielded sizable nuggets including the largest found in Alaska (294-ounce nugget from Swift Creek discovered in 1998). Nuggets were also found nearby at Long, Poorman and Moose creeks. The presence of large nuggets suggests a possibility of nearby hidden rich lodes.
|Location map of Donlin Creek discovery in SW Alaska|
Seventy-five to 100 miles southwest of McGrath, gold placers at Snow Gulch and Julian Creek were found in the Georgetown district - these would later become known as the Donlin Creek deposit. Gold is also found in nearby Omega, Lewis, Quartz, Ruby and Queen Gulch. This region attracted the interest of geologists because of pristine the gold flakes found in the streams by prospectors and the fragile gold nuggets which suggested a nearby source. As a result, WestGold began exploration in this region in 1988 which led to discovery of a large, disseminated, gold deposit with associated with anatomizing granodiorite to rhyolitic dikes intruded into graywacke (Hausel, 1988, 1989a). Drilling over several years identified proven and probable resources of 29.5 million ounces with an additional indicated resource of 10 million ounces. This was an Elephant (so to speak in the exploration business)! Donlin Creek has a gold resource similar in value to the legendary Homestake mine in South Dakota which produced 41 million ounces over a century of mining. Donlin Creek also hosts as much gold as has been mined in all of Alaska from 1869 to 2007!
The Northern Miner reported Donlin Creek to be one of the largest undeveloped gold deposits in the world and the largest undeveloped gold deposit in North America. Based on 2009 plans, the property could become one of the largest gold mines in the world. Mine permit applications were submitted in 2009 and mine construction proposed by 2012.
The deposit consists of felsic sills and dikes that host gold in association with sulfides, quartz veinlets and breccias. Higher gold values are associated with arsenopyrite, stibnite and quartz in dikes and sills that intrude a thick sequence (>5000 feet) of folded Cretaceous graywacke, sandstone and shale. Plans are for a mine to yield 1.5 million oz/yr from ore averaging 0.07 to 0.08 opt Au.
|Flying into Flat, Alaska for July 4th |
Other interesting anomalies in this region include gold at Julian Creek about 25 miles to the northeast with nearby felsic dikes in a similar setting as Donlin Creek, and mercury-gold anomalies at DeCourcy, about 8 miles west and placer gold at Flat Creek about 25 miles to the north-northeast are also of interest (Hausel, 1989b). While recently watching Gold Rush, Alaska on the discovery channel, I can't help but laugh at the antics of these wannabee miners.
Everything they do is exactly backwards of how gold prospecting and mining is done. It is very unfortunate that the Discovery Channel picked such inept miners to educate the public on gold mining and prospecting. There are lots of good gold prospects in Alaska, but one does not go out and buy a half-million dollars in mining equipment before these deposits are sampled.
At Donlin Creek, we found gold spread over a few miles (visit Donlin Creek, Alaska on Google Earth). Donlin Creek consists of northeast-trending mineralized dikes and sills in a region 1.2 miles wide and more than 5 miles long (T. 23 N., R. 49 W). The lode is Alaska's largest gold deposit which runs along a ridge east of Crooked Creek at the heads of Lewis, Queen, Ruby, and Snow Gulches. The deposit consists of calcareous shale and graywacke of the Upper Cretaceous, Kuskokwim Group which strike west-northwest and dip 10-50 degrees SW and are cut by a swarm of Tertiary age rhyodacite to granite-porphyry sills and dikes that trend northeast (Hausel, 1988, 1989). Late northeast and northwest-striking, high-angle faults offset the mineralized zones (Miller and Bundtzen, 1994; Vaillancourt, 2002; St. George, 2004).
The deposit is developed in felsic dikes and sills, with lesser amounts of mineralization in graywacke, particularly where north-northeast trending fault zones intersect mineralized felsic intrusions and graywacke host rocks. The ore minerals are primarily gold-bearing arsenopyrite and arsenian pyrite which are disseminated in the felsic igneous rocks and in veins and networks of veinlets in the igneous and sedimentary rocks (Hausel, 1989b). The veins and veinlets consist of quartz and carbonate gangue, with gold and several ore minerals. The gold occurs mainly in arsenopyrite and stibnite (Hausel, 1989b). In addition minor chalcopyrite, cinnabar, cassiterite, covellite, galena, marcasite, molybdenite, native arsenic, pyrrhotite, sphalerite, scheelite occur in minor amounts.
|Dr. Paul Graff admires old hydraulic 'Giant' at Fullerton|
Alaska in 1988.
The gangue and alteration minerals include crystalline and chalcedonic quartz, carbonate minerals and dickite. Garnet and high tin in some granite porphyry dikes indicate that at least part of the intrusive suite is peraluminous. Based on crosscutting relationships, altered carbonated mafic dikes initially intruded followed by intermediate and felsic dike intrusion. Other than clay, weak sericitic alteration and disseminated sulfides, there is little evidence of thermal alteration of the host rocks (Bundtzen and Miller, 1997). Miller and Bundtzen (1994) report that the felsic dikes vary from 65 to 71 Ma. Gold is disseminated in sulfides, sulfide veins, and in quartz-carbonate-sulfide veining in sericitically-altered igneous rocks (Hausel, 1989b, Szumigala and others, 2000). There is a positive correlation between high fracture density, alteration, and the amount of gold.
Ore shoots are developed in dilatant zones along normal faults where faults steepen in felsic intrusions and graywacke. Alteration assemblages include sericite, illite, kaolinite. dickite, carbonate and pyrite (Hausel, 1989b, Szumigala and others, 2000). Current drilled resources places this deposit in the top 30 gold deposits known in the world (Novagold Press release, January 28, 2002). Its as large as the Homestake deposit, where more than 41 million ounces of gold were mined over a 100 year period.
|Rehealed breccia of Kuskokwim graywacke adjacent to mineralized dikes.|