SNIPE BAY COPPER-NICKEL-COBALT DEPOSITS

By Jeffrey Y. Foley

**********************************************Field Report, December, 1989

UNITED STATES DEPARTMENT OF THE INTERIOR

Manuel J. Lujan, Secretary

BUREAU OF MINES

T S Ary, Director

SNIPE BAY COPPER-NICKEL-COBALT DEPOSIT

INTRODUCTION

The Snipe Bay copper-nickel-cobalt property, at the southwest end of Baranof Island insoutheast Alaska, contains disseminated, massive, and semimassive sulfides of copper, nickel,cobalt, and iron in two mineralized gabbro bodies. Based on diamond drilling by InspirationDevelopment Company, the property is estimated to contain 94,000 short tons with 0.94 pct Cuand 0.34 pct Ni. Available cobalt assay data is insufficient for cobalt grade estimates, but limitedsampling, analyses, and combinations of gravity and flotation tests by the Bureau indicate thatcobalt is widespread in the Snipe Bay deposits and is recoverable. Platinum and palladium werealso detected in samples collected by the Bureau in 1988.

The Bureau visited the Snipe Bay property on several occasions during the last twodecades. T.L Pittman (Mining Engineer, Alaska Field Operations Center) visited the property in1963 and mapped the southernmost gabbro body, which had only been discovered during thepreceding year. A bulk sample was collected by AFOC in 1981 for mineral characterization andpreliminary flotation concentration tests by Albany Research Center (ALRC). In 1988, AFOCcollected an additional five samples for further characterization and beneficiation tests by Salt LakeCity Research Center (SLRC).

LOCATION AND ACCESS

Snipe Bay is located along the densely forested southwest coast of Baranof Island, insoutheast Alaska (fig. 1). The Snipe Bay deposits are between the 170-and 600-ft-elevations in asteep, south-facing gully near the mouth of Snipe Bay (fig. 2). Sitka, 45 air miles north-northwest ofSnipe Bay, is the nearest supply and transportation center. A small lake ("Stol Lake"), 1.5 milesnorth of the deposit, has been used to land small float planes in the past, but, at least one aircrafthas crashed and local pilots are not willing to attempt landings there. There are no roads in theregion and because there are no safe boat- or float plane-landing sites along the rugged northshore of Snipe Bay, helicopter transport from Sitka provides the most practical access to thedeposit.

LAND STATUS

The Snipe Bay deposit is in the Tongass National Forest, administered by the NationalForest Service, and is open to mineral entry, with possible restrictions as dictated by the ForestService (Roberts, 1984). There are currently no active mining claims on the deposit.

PROPERTY HISTORY

In 1922, four federal mining claims were located at the deposit by 1. Myre Hofstad. In 1929,A.F. Buddington, of the U.S. Geological Survey was the first government geologist to examine theSnipe Bay property. In 1939, the Snipe Bay claims were acquired by S.H.P. Vevelstad, wholocated an additional six claims. The deposit was further examined in 1941 by J.C. Reed and G.O.Gates of the Geological Survey (Reed and Gates, 1942). During that examination, thenorthernmost of the two mineralized gabbro bodies was mapped and sampled. The propertychanged ownership several times in the next two decades and claims were maintained undervarious option agreements. T.L. Pittman, Bureau of Mines Mining Engineer, examined the property

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Figure 2. - Map of Snipe Bay area. Base from U.S. Geological Survey Port Alexander (B-3 and B-4)Quadrangle

in 1963, and extended geologic map coverage and sampling to cover the southern gabbro body,which was discovered in 1962 by Donald MacDonald, owner at that time. In 1973, InspirationDevelopment Company acquired an option on the property and located an additional 107 miningclaims. Assessment work by the earlier owners consisted of clearing vegetation, trenching, andsampling; Inspiration Development Company constructed two buildings, excavated additionaltrenches, and delineated two mineralized gabbro bodies on the property with 21 diamond-drillholes. Assessment work was maintained on the property until 1979, when the claims were allowedto lapse by Robert M. Johnson, the most recent property owner. The buildings constructed byInspiration Development Company were burned by the National Forest Service in 1984.

T.L. Pittman and J. Still, Bureau of Mines Mining Engineers, visited the property again in1981 and collected a high grade, 135-lb bulk sample from an exposed sulfide mass at about the290-ft-elevation. Mineralogical characterization and preliminary flotation tests were performed onthat sample by the Bureau's Albany Research Center. Bureau of Mines Geologists, Arne Bakkeand J.Y. Foley visited the property again in 1988 and collected five more samples, totalling about400 lb, for further characterization and beneficiation tests by the Bureau's Salt Lake ResearchCenter.

GEOLOGY

The Snipe Bay area is underlain by the Jurassic-Cretaceous Sitka Graywacke which alsounderlies much of western Baranof, Kruzof, Chichagof, and Yakobi Islands. The Sitka Graywackeincludes two major rock types: a massive, thick-bedded graywacke and thin- to medium-bedded,alternating and intergrading argillite and graywacke. Minor lithologies include argillite laminae, thingraywacke beds, conglomerate, and breccia. The entire sequence is several thousand feet thickand is classified as a turbidite assemblage (Loney and others, 1975). The Sitka Graywackedisplays contact metamorphic aureoles and a schistose fabric where intruded by Tertiary plutons.A few miles east of Snipe Bay and elsewhere on Baranof Island, the Sitka Graywacke conformablyoverlies the Khaz Formation, which is assigned to the Triassic-Jurassic Kelp Bay Group. The KhazFormation is composed of a chaotic assemblage of greenstone, greenschist, graywacke, andphyllite.

Copper-nickel-cobalt deposits occur in Tertiary gabbro, norite, and associated ultramaficintrusive rocks at Snipe Bay and several other locations in southeast Alaska, including the BradyGlacier deposit in the Crillon-La Perouse mafic complex in the Fairweather Range, Bohemia Basinand related deposits on Yakobi Island, Mirror Harbor on Chichagof Island, Fleming Island, and atFunter Bay on Admiralty Island (Buddington, 1926, Reed, 1936, Reed and Van N. Dorr, 1942, Reedand Gates, 1942, Barker, 1963, Rossman, 1963, Plafker and MacKevett, 1971, Czamanske andothers, 1981, Himmelberg and Loney, 1981, Thornsbery, 1982, and Still, 1988).

At Snipe Bay, four sulfide-rich concentrations have been exposed in three trenches andone cliff exposure by past property owners; these are referred to in this report as the upper andlower north trenches, the upper south trench, and the lower south exposure. Figure 3 is adaptedfrom brunton and tape maps constructed by Gates and Reed (1942) and Pittman (unpublishedBuMines data) and shows the geology and the relative positions of these trenches. The upper andlower north trenches are in the northernmost of two altered gabbro bodies and the upper southtrench and the lower south exposure are in the southernmost of the two gabbro bodies. A third,small gabbro body crops out along the beach to the south of the sulfide deposits. Sulfide-bearinggabbro float was reported by T.L. Pittman, 1.5 miles to the north of the deposit. When examined in1988, all but the lower south trenches were mostly overgrown with vegetation, but sulfide-richrubble was observed at the surface and the original trench-sites were readily recognizable.

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Figur 3. -SrnIpe Bay copper-nickel cobalt deposlts. Baranol Island, Alaska. Base map andgeolog adapted from Reed and Gales (1 942) and Pittman ( 963. unpublihed).

The upper and lower gabbro bodies are both sinuous in plan view and they strike up thesteep, south-facing gully on the north side of Snipe Bay. The gabbro at Snipe Bay is typically verycoarse-grained and according to petrographic descriptions by Reed and Gates (1942), primaryferromagnesian silicate minerals are largely altered to brown hornblende which is in turn partiallyaltered to pale actinolite; calcic plagioclase is altered to albite and oligoclase. Magnetite isabundant and forms between 10 and 25 pct of the rock. Apatite is reported to make up between 1and 2 pct of the rock, and is concentrated in soda-rich feldspars. Other reported gangue mineralsinclude ilmenite, chlorite, biotite, malachite, and iron oxides, including limonite, and goethite.

At the margins of the Snipe Bay gabbro bodies, the Sitka Graywacke has beenmetamorphosed to quartz-biotite schist, biotite schist, quartzite, amphibolite, and porphyroblasticcordierite schist.

DEPOSIT DESCRIPTION

Sulfide minerals are widespread throughout the north and south gabbro bodies and areconcentrated as disseminated, semimassive, and massive segregations at the four sites mentionedabove. In decreasing order of abundance, sulfide minerals at Snipe Bay include pyrrhotite,chalcopyrite, pentlandite, pyrite, marcasite, and siegenite, a mineral in the linnaeite group with acomposition of (Co,Ni)3S4 (Reed and Gates, 1942 and unpublished BuMines data). L.L. Brown,ALRC Geologist, reported a few grains of franklinite in a sulfide-rich sample collected from theupper south trench by J. Still. During microprobe and scanning-electron microscope examinationof that sample, Mr. Brown also detected up to 4 pct cobalt in pentlandite, which rims pyrrhotite. Asilver-colored mineral that resembles carrollite [Cu(Co,Ni)2S4] (or siegenite, also in the linnaeitegroup), In megascopic appearance and under a hand lens, is fairly abundant in samples collectedin 1988 from the upper north and lower south trenches.

Reed and Gates (1942) originally estimated the Snipe Bay deposit to contain 430,000 stwith an average grade of 0.3 pct each, copper and nickel. Those estimates were based entirely onsurface data. Reed and Gates estimated the gabbro body to be 256 ft long, 125 ft wide, and toextend to a depth of 135 ft beneath the lowest point of outcrop.

Diamond drilling, by Inspiration Development Company showed that the deposits do notextend to the depth inferred by Reed and Gates. Vance Thornsberry, Consulting Geologist,Spokane (WA) performed the exploration program for Inspiration Development Company. Mr.Thornsberry reports that mineralization persists to only a shallow depth where a less mafic, barren,dioritic rock containing quartz, hornblende, and possibly biotite was encountered (personalcommunication, December 18,1989).

Based on the diamond drilling and magnetometer data, Mr. Thornsberry estimated the twogabbro masses to contain 94,000 short tons of mineralized rock. Total weighted grade estimatesare 0.94 pct Cu and 0.34 pct Ni. The northern body is estimated to contain 51,000 short tons at0.368 pct Cu and 0.114 pct Ni. The southern mass is estimated to contain 43,000 short tons at1.63 pct Cu and 0.64 pct Ni.

Mr. Thornsberry also reports that a mineralized gabbro body, similar in size and characterto the masses at Snipe Bay, occurs at tidewater along "Brownie Bay", in the next small inlet to thenorth, on the west coast of Baranof Island. Also, magnetometer and analytical data for soilsamples indicate that another sulfide-bearing gabbro body occurs to the south and uphill from thesmall lake, 1.5 mi northeast of the Snipe Bay deposits. The latter is in the vicinity of the sulfide-bearing gabbro float reported By. T.L Pittman.

AFOC 1988 FIELD INVESTIGATIONS

Four days were spent at the Snipe Bay property in October, 1988. During that time, fivebulk sulfide-bearing gabbro samples, several geochemical samples, and numerous specimenswere collected from four trenches in sulfide-bearing gabbro. Geochemical analyses andpetrographic descriptions are reported in table 1.

TABLE 1.- Geochemical analyses and descriptions for Snipe Bay samples

ElementAs Au Co Cr Cu Ni Pd Pt V

Sample oom Dob oom oom ppm opm ppb gpb opm

SU26045 54 11 40 419 5583 1154 4 20 539SU26047 <5 9 593 2249 3236 10859 440 100 450SU26048 8 4 104 373 2140 810 4 15 609

Sample Descriptions

SU26045 Composite chip sample collected over 50-ft widthat lower north trench. Semimassive anddisseminated chalcopyrite, pyrrhotite, and bornitein medium- to coarse-grained altered gabbro.

SU26047 Composite chip sample collected over 100-ft widthat lower south sulfide exposure. Semimassivechalcopyrite and pyrrhotite in fine-grainedgabbro.

SU26048 Composite chip collected from 50-ft width at uppernorth trench. Disseminated pyrite, marcassite,chalcopyrite and carrollite or siegenite.

BENEFICIATION

Sulfide flotation concentrates were produced at ALRC and SLRC on bulk samples fromSnipe Bay. SLRC also performed table tests on several samples. ALRC performed flotation testson a 135-lb, high-grade sample collected by Pittman and Still at about the 290-ft elevation. Thiscorresponds to the elevation of the lower south sulfide exposure where disseminated and semi-massive to massive sulfides occur. The results of these tests are shown in table 2. SLRCperformed flotation and gravity separation tests on 5 bulk samples, weighing from 50 to 200 lbeach, from the four mineralized areas. The sample locations, grinding procedures, times,reagents, and other pertinent data are listed in tables 2-12. Tables 13 and 14 contain summarydata for the flotation and tabled concentrates from all the tests.

RECOMMENDATIONS

This report is to be forwarded to SLRC where additional beneficiation procedures arescheduled to be completed on the bulk samples collected in 1988. SLRC is planning to publish theresults of those tests in a Bureau of Mines Report of Investigation.

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Sample Name PFLOTAT.JN SLC Sample Number _________

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rEST NUMBER 2 4'2 DATE LI

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tEMARKS:

Table 13. - Flotation concentrate summary data

Ag Au Co Cu Fe Ni Pd Pt SsamDle location concentrate oz/st OZ/st DCt Dct DCt DCt oz/st OZ/st DCt1S147 lower south rougher 0.215 0.007 0.16 9.24 30.0 2.49 <0.001 <0.001 27.21S147 lower south scavenger .068 .004 .10 .20 47.7 1.74 <.001 <.001 31.326048 upper north rougher .04 1.6 .2526045 lower north rougher .04 3.6 .4326066 lower north rougher .13 4.6 2.3826049 upper south rougher .08 10.7 1.5726047 lower south rougher .07 11.4 .95

Table 14. - Tabled concentrate summary data

Au Co Cu Ni Pd Pt Tisample location oz/st Dct Dct oct oz/st oz/st DCt26048 upper north 0.3 0.2 0.047 30.126045 lower north .008 .32 .037 31.026066 lower north .18 4.9 3.19 5.0926049 upper south .015 .8 .12 29.126047 lower south .016 1.9 .079 27.6

This report is also being provided to the AFOC Juneau Branch. It is recommended thatthat office consider additional work on the Snipe Bay, "Brownie Bay", and 'Stol Lake" deposits.Such future work could be performed in conjunction with mineral resource evaluation studies inthe Tongass National Forest or Chichagof Mining District. Additional information on these threeareas is forthcoming from Vance Thornsberry.

Roger Burleigh, in the AFOC Fairbanks Section, who is studying advanced metals inAlaskan ore deposits may also wish to perform additional analyses on samples from the Snipe Bay,"Brownie Bay", and "Stol Lake" deposits.

Additional analytical data for gold and platinum-group metals has been requested for thegravity and flotation concentrates produced at SLRC. These data will be forwarded to the JuneauBranch upon receipt.

REFERENCES

Barker, Fred. The Funter Bay Nickel-Copper Deposit, Admiralty Island, Alaska. U.S.Geological survey Bull. 1155, 1963, pp. 1-10.

Buddington, A.F. Mineral Resources of Alaska. U.S. Geological Survey Bull. 773, pp. 106-107.

. Mineral Investigations in Southeastern Alaska. Ch. in U.S. Geol. Survey Bull. 783,1926, pp. 41-47.

Czamanske, G.K., Joseph Haffty, and S.W. Nabbs. Pt, Pd. and Rh Analyses andBeneficiation of Mineralized Mafic Rocks from the La Perouse Layered Gabbro, Alaska. EconomicGeology, vol. 76, 1981, pp. 2001-2011.

Himmelberg, G.R. and R.A Loney. Petrology of the Ultramafic and Gabbroic Rocks of theBrady Glacier Nickel-Copper Deposit, Fairweather Range, Alaska. U.S. Geological Survey Prof.Paper 1195, 1981, 26 pp.

Loney, R.A., D.A. Brew, L.J.P. Muffler, and J.S. Pomeroy. Reconnaissance Geology ofChichagof, Baranof, and Kruzof Islands, Southeastern Alaska. U.S. Geological Survey Prof. Paper792, 1975, 105 pp.

Pittman, T.L. Unpublished BuMines data summarizing 1963 Snipe Bay sampling results.Available from J.Y. Foley, Bureau of Mines, Fairbanks, Alaska.

Plafker, George, and E.M. MacKevett, Jr. Mafic and Ultramafic Rocks from a LayeredPluton at Mount Fairweather, Alaska. Ch. in U.S. Geological Survey Prof. Paper 700-B, 1971, pp.B21 -B26.

Reed, J.C. Nickel Content of an Alaskan Basic Rock. U.S. Geological Survey Bull. 897-D,1939, pp. 263-268.

Reed, J.C. and G.O. Gates. Nickel-Copper Deposit at Snipe Bay, Baranof Island, Alaska.U.S. Geological Survey Bull. 936-M, 1942, pp. 321-330.

Reed, J.C. and J. Van N. Dorr, 2nd. Nickel Deposits of Bohemia Basin and Vicinity, YakobiIsland, Alaska. U.S. Geological Survey Bull. 931-F, 1942, pp. 105-138.

Roberts, W.S. Availability of Land for Mineral Exploration and Development inSoutheastern Alaska, 1984. BuMines Special Publication, 1985, 34 pp.

Rossman, D.L Geology and Petrology of Two Stocks of Layered Gabbro In theFairweather Range, Alaska. U.S. Geological Survey Bull. 1121-F, 1963, 45 pp.

Still, J.C. Distribution of Gold, Platinum, Palladium, and Silver in Selected Portions of theBohemia Basin Deposits, Southeast Alaska (with an appendix section on Mirror Harbor). U.S.Bureau of Mines Open-File Report 10-88, 1988, 42 pp.

Thornsberry, V.V. Bohemia Basin Nickel-Copper Property, Southeast Alaska. ALECOMining Group Prospectus, 1982, unpaginated.