Divide Prospect, Nome Mining District, Nome Census Area, Alaska, USAi

Regional Level Types
Divide Prospect	Prospect
Nome Mining District	Mining District
Nome Census Area	Census Area
Alaska	State
USA	Country

Location: The Divide prospect is due south of Boer Creek (NM049). It is approximately bounded on the west by Quartz Creek (NM111); it is north of Divide Creek (NM057) and west of the Campion Ditch. The prospect area extends north nearly 1 mile long and is more than one-half mile wide. The location given is the approximate center of this large mineralized area that extends across a low hill (locally called Boer Mountain) that is about 1,425 feet high.
Geology: The most extensive work on the Divide prospect dates from the 1990,s (Chris Gierymski, Cominco American, written communication, December 1995). In 1994, David and Daniel Lajack established a 2,000- by 2,500-foot soil-sample grid on the southeast flank of Boer Mountain, the hill at the head of Boer Creek (NM047). Seventeen of 57 soil samples contained 100 ppb or more of gold; the highest content was 370 ppb gold. In 1995, Cominco expanded the grid to a 1- by 1.5-mile area elongated to the north, collected almost 700 soil samples, and ran VLF and ground magnetics. A series of 21 trenches was also dug at this time, with a total length of 5,822 feet. About 1,000 samples were collected from the trench system. At least two major northeast-trending vein zones were found as a result of Cominco's exploration effort. Trench 1 trends east; it starts about 1,300 feet east of Quartz Creek approximately on the section line between sections 26 and 35 on the southeast flank of Boer Mountain. One- to 3-foot-wide gold-bearing quartz veins that strike northeast and dip nearly vertically were mapped and sampled near trench 1. The channel samples along a 50-foot interval in trench 1 assayed 0.663 ounce of gold per ton. The trench was partly frozen; strong 'muck' anomalies were found along the trench in three sections that aggregated 250 feet in length. Trench D-12 cut approximately the same zone as trench 1, and it was also well mineralized. Trenches D-10 and D-11 were cut nearly on the divide between Quartz Creek and Boer Creek; these trenches also found quartz veins that strike northeast and dip steeply to shallowly. Trench 10 found a maximum of 8 feet of 0.047 ounces of gold per ton; trench D-11 contained 55 feet of 0.437 ounce of gold per ton and 40 feet of 0.044 ounce of gold per ton, including an interval of 20 feet that contained 0.080 ounce of gold per ton. Trench D-9, north of trenches 10 and 11 and on trend with upper Boer Creek, had a 70-foot interval with 0.024 ounce of gold per ton, including 20 feet with 0.067 ounces of gold per ton. The prospect was drilled by Cominco American in 1996 (written communication, August 22, 1996). In general, drill results were not as good as trench results. Five holes were drilled at the head of the divide between Quartz Creek and Boer Creek. The best drill hole, D-6, intercepted 28 feet that contained 0.011 ounce of gold per ton. Three holes were drilled southeast of Boer Mountain; hole Div-9 contained 10 feet with 0.235 ounce of gold per ton. About 2,000 feet east of Boer Mountain, hole Div-3 had 37 feet with 0.055 ounce of gold per ton, including 24.7 feet with 0.091 ounce of gold per ton. The gold-bearing quartz veins occur along joints and fractures. The veins have albite and local silicified selvages, and larger veins have several feet of selvage with iron-bearing carbonate (ankerite). In general, pyritization appears to be a favorable indication of nearby gold mineralization. In decreasing order of abundance, the ore minerals in the veins are pyrite, arsenopyrite, pyrrhotite, galena, stibnite, sphalerite, and jamesonite. The host rocks at the Divide prospect are metasedimentary rocks of retrograde greenschist or lower amphibolite facies, including graphitic and calcareous schist, blue-gray, gray, and black marble, and black quartz schist and quartzite (Hummel,1962 [MF 248]). Strata west and northwest of Quartz Gulch, including most of the canyon of Boer Creek, are less graphitic. Projection of bedrock geology from the west suggests that some of these metamorphic rocks could be biotite-bearing (Sainsbury, Hummel, and Hudson, 1972; Bundzten and others, 1994). The schistose rocks are mostly phyllonites with slip schistosity approximately parallel to lithologic contacts and original bedding. The schistosity strikes northeast to east-northeast and dips about 30 degrees southeast. The metamorphic rocks here are probably part of the Nome Group derived from Proterozoic to early Paleozoic protoliths (Till and Dumoulin, 1994). The Nome Group underwent regional blueschist facies metamorphism in the Late Jurassic or Early Cretaceous (Sainsbury, Coleman and Kachadoorian, 1970; Forbes and others, 1984; Thurston, 1985; Armstrong and others, 1986; Hannula and McWilliams, 1995). The blueschist facies rocks were recrystallized to greenschist facies or higher metamorphic grades in conjunction with regional extension, crustal melting, and magmatism in the mid-Cretaceous (Hudson and Arth, 1983; Miller and Hudson, 1991; Miller and others, 1992; Dumitru and others, 1995; Hannula and others, 1995; Hudson, 1994; Amato and others, 1994; Amato and Wright, 1997, 1998). Lode gold mineralization on Seward Peninsula is mostly related to the higher temperature metamorphism in the mid-Cretaceous (Apodoca, 1994; Ford, 1993, Ford and Snee, 1996; Goldfarb and others, 1997).
Workings: Extensive surface trenching and some drilling were conducted in the 1990's. Extensive work began in the area in 1994 when the Lajacks conducted a soil survey and located 20 State of Alaska claims. The project as developed by Cominco American included 92 DIV (name) claims, 40 Lost claims, and 17 East claims. Surrounding lands are a patchwork of open state land, claims by competitors, and Native selected land. The DIV claims built on the core staked by the Lajacks. In 1995, Cominco American conducted an extensive trench and soil prospecting program. The best single trench was D-11 at the divide between Quartz Creek and Boer Creek. This trench had 55 feet with 0.437 ounce of gold per ton. Cominco American continued with a drilling program in 1996. In general the drilling program found less gold than surface trenching, although drill results locally indicated significant mineralization, including 10 feet with 0.235 ounce of gold per ton in Div-9 southeast of Boer Mountain and 37 feet with 0.055 ounce of gold per ton in Div-3, about 2,000 feet east of Boer Mountain.
Age: Mid-Cretaceous; veins post-date regional metamorphism and are probably similar in age to other lode gold deposits of Seward Peninsula.
Alteration: Local silicification and pervasive introduction of pyrite and ankerite near vein systems.

Commodities (Major) - Au
Development Status: None
Deposit Model: Low sulfide Au-quartz vein (Cox and Singer, 1986; model 36a).

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Link to USGS - Alaska:	NM058

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References