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File Created: 01-Oct-1987 by Trygve Hoy (TH)
Last Edit:  12-Nov-1991 by George Owsiacki (GO)

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NMI 082M4 Ag4
BCGS Map 082M011
Status Past Producer NTS Map 082M04W
Latitude 051º 08' 40'' UTM 11 (NAD 83)
Longitude 119º 48' 34'' Northing 5669641
Easting 303492
Commodities Silver, Gold, Zinc, Lead, Copper, Antimony Deposit Types G06 : Noranda/Kuroko massive sulphide Cu-Pb-Zn
I05 : Polymetallic veins Ag-Pb-Zn+/-Au
Tectonic Belt Omineca Terrane Kootenay
Capsule Geology

The Samatosum deposit is located in structurally complex metasedimentary and metavolcanic rocks of the Paleozoic (Lower Cambrian and older(?) to Mississippian) Eagle Bay Assemblage (Formation). The assemblage has a complex deformational history involving multiple stages of thrust faulting and folding during the Jura-Cretaceous which produced strongly foliated and overturned rocks trending northwest and dipping northeast. These Paleozoic rocks are intruded by mid-Cretaceous granodiorite and quartz monzonite (such as the Baldy batholith about 30 kilometres to the north of the deposit), and Early Tertiary quartz-feldspar porphyry, basalt and lamprophyre dykes. These are all locally overlain by Miocene plateau lavas, now represented in the area by occasional erosional remnants.

The deposit area can be divided into several northwest trending, northeast dipping units. From northeast to southwest these are: 1) the Tshinikan Limestone which forms steep, massive landforms dominating the area; 2) mixed sediments consisting of interbedded cherts and argillite; 3) mafic volcanics; 4) the "Mine Series" of rocks which consist of a zone of more mixed sediments and mafic volcanics, with minor felsic to intermediate volcanics, which form the host stratigraphy for both the Samatosum and Discovery or Rea Gold zone (082M 191) deposits; and finally 5) a thick unit of argillites and wackes and a package of felsic rocks which lie in the structural footwall of the Mine Series.

The generalized ore stratigraphy reveals the apparent stratabound nature of the orebody within the hanging wall portion of the heavily strained and highly altered Mine Series rocks. The orebody lies near the interface of altered mixed sediments and predominantly altered argillites/wackes. Original terms such as "sericitic tuffs" for the mixed sediments, and "muddy tuffs" for the altered argillite/wackes are now largely out of favour as it is really alteration products that one sees rather than original lithologies (Friesen, 1990).

The mixed sedimentary unit (SERT) is characterized by a strong yellow to white sericitic content, interbedded with up to 30 per cent cherty/quartz lenses. The altered argillites (MUT) are characterized by light silvery grey muscovite and sericite. They may also often locally contain up to 60 per cent very fine-grained pyrite and host low grade values of base and precious metals. Both units represent altered lithologies; their protoliths were probably variations of an original argillite/wacke/tuff sequence.

Both the SERT and MUT lie structurally below a thick unit of chloritic mafic volcanics, which in the deposit area are most commonly tuffaceous to lapilli in texture; but with an occasional pillowed component.

Both the Samatosum and original Discovery zone or Rea Gold zone (082M 191) 500 metres to the southwest are contained in a very similar stratigraphy: within a package of mixed sediments, argillites and their sericitic equivalents of SERT and MUT, and both are structurally overlain by mafic pyroclastics. There is much speculation regarding their structural and genetic associations. There is a strong suggestion of repetition by folding and/or faulting (which supports a long favoured theory of a thrust fault zone located between the deposits). Alternatively, but currently discounted, the two deposits may exist within similar stratigraphic cycles overprinted by a crosscutting alteration package (Friesen, 1990).

The Samatosum deposit is an early, highly deformed quartz vein system containing massive to disseminated components of tetrahedrite, sphalerite, galena and chalcopyrite hosted in structurally complex wallrocks. The upper portion of the orebody is tabular, averages about 5 metres in thickness, has a northwesterly strike length of about 500 metres and dips at an average of 30 degrees northeasterly for 100-150 metres. In the northern half of the deposit the tabular nature of the orebody gives way downdip to an apparent synformal structure, which is currently interpreted to be caused by slicing and imbrication by local overturning and thrust faulting. The northern half of the orebody has a northwesterly plunge of about 20 degrees, whereas the southern half displays a very slight plunge to the southeast (phase 2 folding?).

Tetrahedrite is the most valuable mineral in the ore zone, followed by sphalerite, chalcopyrite and galena. The tetrahedrite contains 36 per cent copper, 25 per cent sulphur, 23 per cent antimony, 5 per cent zinc, 4 per cent silver, 3 per cent arsenic and 2 per cent iron. Tetrahedrite appears to be the most uniformly distributed, while the sphalerite, galena and chalcopyrite often appear more erratically distributed in the northern end of the orebody as semimassive to massive lenses within the quartz vein host; perhaps indicating more than one mineralizing episode. It is important to note to note that whereas chalcopyrite, sphalerite and galena can be present in minor amounts in virtually any quartz vein occurrence throughout the property; tetrahedrite has so far been rarely found outside the immediate ore zone (Friesen, 1990).

The principal ore-related gangue minerals are quartz (30 per cent), dolomite (19 per cent) and pyrite (11 per cent).

Sericite and muscovite are by far the dominant alteration minerals in the Mine Series rocks and are thought to be a deformational product of the original ore-related alteration. All units from the lower portion of the mafics through the entire Mine Series stratigraphy are sericitic. Muscovite/sericite alteration fronts producing MUT commonly crosscut bedding and foliation, often leaving behind unaltered argillite/wacke remnants.

Other significant alteration in the deposit area includes: silicification or silica flooding of portions of wallrock surrounding the orebody (eg. many original "quartzites" and black cherts are now believed to be silicified MUT and argillites); dolomite, much more intense than previously believed, the bulk of which is probably a late-stage fault-related overprint; pyritization, as a replacement feature of lapilli in the mafic pyroclastics; and the green mica fuchsite, so far almost entirely restricted to a several metre thick occurrence associated with the argillites/MUT along the immediate sheared footwall portion of the ore zone.

Underground mineable reserves at Samatosum are 80,278 tonnes grading 1.2 per cent copper, 2.9 per cent zinc, 1.7 per cent lead, 1021.5 grams per tonne silver and 1.7 grams per tonne gold (Northern Miner - August 5, 1991). Both open pit and underground reserves are expected to be exhausted by October 1992. The underground reserve is the strike extension of the open pit deposit and extends approximately 198 metres beyond the pit wall before it is structurally terminated.

The Samatosum deposit was discovered in 1986. During 1988 a feasibility study determined the deposit could be mined economically by open pit methods, despite an unusually high 25:1 waste-to-ore stripping ratio. Mine stripping began in March 1989; ore production and milling began in May 1989; shipments began in June 1989.

Mining ceased in July 1992 and milling ceased in September 1992.

EM FIELDWORK 1998, pp. 287-306
EMPR ASS RPT 12737, 14185, 18571, 19199, 19200, 21689
EMPR ENG INSP Annual Report 1989, 1990
EMPR EXPL 1983-xxxii, 157; 1986-B7-B19,C113
EMPR FIELDWORK 1984, pp. 67-83; 1985, pp. 59-68
EMPR MAP 56; 65 (1989)
EMPR OF 1992-1; 1998-9; 1998-10; 1999-14; 2000-31
EMPR PF (Friesen, R.G. (1990): Geology of the Samatosum Deposit - Field Trip B2, GAC-MAC Joint Annual Meeting, Vancouver 1990, Mineral Deposits of the Canadian Cordillera; Preliminary Engineering Geology, Hydrogeology and Rock Mechanics Assessments for the Proposed Underground Mine, Samatosum Project - May 1991; Memorandum to Geological Survey Branch, P. Schiarizza - June 14, 1990; Press Release, Rea Gold Corporation, Feb.21, 1991; M.E.G Luncheon Talk notes, Jan.13, 1988)
GSC MAP 48-1963; 5320G
GSC OF 637
CMH 1987-88, pp. 272,330
GCNL #4,#57,#131,#135,#153,#172,#177,#210, 1986; #8,#76,#96,#108, #111,#112,#116,#117,#118,*#133, 1987; #33,#70,#78,#207, 1988; #1(Jan.3),#56(Mar.21),#123(June 27),#205(Oct.25), 1989; #19(Jan.26),#52(Mar.14),#90(May 9),#179(Sept.17),#186(Sept.26), 1990; #38(Feb.22),#52(Mar.14),#68(Apr.9),#127(Jul.3),#147(Jul.31), #200(Oct.17), 1991
IPDM Feb. 1986
N MINER Dec.30, 1985; Jan.13, March 31, July 14,21, Aug.4, 1986; Jan. 26, May 11, 1987; March 7, May 2,23, Oct.24, 1988; June 5,12, Nov.6,13, 1989; Feb.6, Mar.19, Sept.10, 1990; Apr.1,15, May 6, Jul.15, Aug.5, Oct.21, 1991
N MINER MAG *June 1989, pp. 15-18
NAGMIN Jan.15, March 30, July 6, Nov.9, 1984
NW PROSP Jan. 1987
V STOCKWATCH Nov.28, 1986; May 22,28, July 13, Dec.17, 1987
Dickie, G.J., Preto, V.A. and Schiarizza, P. (1986): Mineral Deposits of the Adams Plateau - Clearwater area
Pirie, I. (1988): Geology and Mineralization of the Samatosum (Rea Gold) Deposit, Adams Plateau, B.C., MEG Talk, January 1988 - Notes taken by T. Schroeter and C. Lund
Preto, V.A. and Schiarizza, P. (1985): Geology and Mineral Deposits of the Adams Plateau - Clearwater Region - GSA Cordilleran Section Meeting, May 1985, pp. 16-1 to 16-11