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File Created: 08-Apr-1992 by Dave Nelles (DMN)
Last Edit:  05-May-1992 by Dave Nelles (DMN)

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NMI
Name CHRISTA, COQUIHALLA, AURA Mining Division Similkameen
BCGS Map 092H055
Status Showing NTS Map 092H11E
Latitude 049º 30' 59'' UTM 10 (NAD 83)
Longitude 121º 01' 08'' Northing 5486749
Easting 643395
Commodities Gold, Silver Deposit Types I02 : Intrusion-related Au pyrrhotite veins
Tectonic Belt Intermontane Terrane Plutonic Rocks, Overlap Assemblage
Capsule Geology

The Christa occurrence, discovered in 1988, is located three kilometres east of the summit of Coquihalla Mountain near the headwaters of Jim Kelly Creek.

The Coquihalla Mountain area is underlain by intermediate to felsic flows and pyroclastic rocks assigned to the Late Oligocene to Early Miocene Coquihalla Formation, which unconformably overlie intrusive rocks of the Late Jurassic and Early Cretaceous Eagle Plutonic Complex.

The Christa occurrence consists of several small outcrops of quartz breccia hosting quartz veins and veinlets within a brecciated phase of the Eagle Plutonic Complex, which is here characterized by either muscovite granite or gneissic granodiorite. These rocks are overlain by younger tuff of the Coquihalla Formation less than 50 metres to the north.

The poorly sorted breccia comprises angular to subrounded, clear to milky quartz fragments, up to 30 centimetres in diameter, in a siliceous matrix. It hosts no visible sulphides, but limonite alteration, varying from one to five per cent of the total rock, has resulted in widespread pervasive orange staining. Local, less than five-millimetre wide grey quartz veins, cut both the fragments and the matrix, and are themselves cut by late milky quartz veins. Traces of electrum were tentatively identified in thin section.

There is very little difference mineralogically between the fragments and the matrix, both of which are made up of 70 to 80 percent quartz and 15 to 25 per cent sericite. This suggests that both were derived from the same material. Late quartz veins, and most probably pyrite, appear to have been introduced after brecciation occurred.

The breccia is believed to have been the product of various stages of a multi-phase process of diffuse silicification and sericitization, stockwork quartz veining, fragmentation, late quartz veining and further brecciation. The original protolith has not been determined.

Sixty three, 1.5-metre wide continuous chip samples across the largest quartz breccia outcrop averaged 0.514 grams per tonne gold and 5.4 grams per tonne silver, including a 13.5-metre interval which graded 1.034 grams per tonne gold and 9.6 grams per tonne silver (Assessment Report 20488).

Bibliography
EMPR ASS RPT 10868, 14362, *19446, *20488
EMPR EXPL 1982-170; 1986-C219
GSC MAP 737A; 12-1969; 41-1989
GSC P 69-47; 88-E1, pp. 177-183

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