Here is what CBA is pinning their hopes on in the Year 2000...this is an excerpt from the 1988 Resident Geologists' Report of Activities...I wish them luck!
Entwine Lake Intrusion
The Entwine Lake Intrusion covers 200 square km in the Eagle Rock Lake area 75 km south of Dryden, and lies within the Irene-Eltrut Lakes batholithic complex. Davies (1965) identified three major phases: an augite syenodiorite that occupies the eastern arm of the intrusion; a biotite-augite diorite in the main (western) part of the intrusion; and also in the main part of the intrusion, a porphyritic monzonite. A narrow rim of amphibolite that surrounds the northern, western, and southern edges of the intrusion, was interpreted by Davies (1965) to be basalt flows into which the intrusion was emplaced. A small body of hornblende peridotite occurs in the centre of the intrusion. Three sulphide occurrences are indicated on Davies' (1965) map, distributed around and close to the edge of the intrusion. A fourth sulphide showing, the Jock Lake Occurrence, not identified by Davies' reconnaissance mapping. was subsequently discovered in the northern part of the intrusion, within the biotite-augite diorite.
JOCK LAKE OCCURRENCE
The Jock Lake Occurrence was investigated by Noranda Mines Ltd. from 1969 to 1974. Electromagnetic, magnetic and I P surveys and ten diamond-drill holes for a total of 3491 feet. were completed on the property. No further work was done at the occurrence until 1986, when reconnaissance by BP Resources Canada Limited indicated anomalous PGE values in samples taken from Noranda Mines' abandoned diamond-drill core. A total of 617 claims were staked, covering the entire intrusion as it was known at that time. An airborne calculated gradiometer and EM survey was flown over the block in 1987. In 1988, detailed geologic mapping and sampling of the Jock Lake Occurrence, claimline reconnaissance mapping, and sampling over the entire claim group was done. Diamond drilling on the Jock Lake Occurrence commenced in November 1988 (G. Campbell. Geologist, BP Resources Canada Limited. personal communication. 1988).
As reported previously (Blackburn et al. 1988), grain samples taken from the occurrence in l987 returned the following ranges on analysis: 200 to 415 ppb gold; 212 to 545 ppb platinum; and 450 to 840 ppb palladium, though considerably higher values have been obtained in detailed sampling programs.
The writer visited the Jock Lake Occurrence in 1988, and the following description incorporates observations made at that lime, augmented by G. Campbell, Geologist, BP Resources Canada Limited (personal communication, 1988). A west northwest-trending, 800 meter long zone of discontinuous sulphide mineralization that contains anomalous PGE is offset by sinistral north-trending faults. The host for the mineralization is a porphyritic gabbro phase of Davies' (1965) biotite-augite diorite. At the eastern end of the zone, the porphyritic gabbro is characterized by a purple colour and is strongly magnetic, possibly representing an oxidizing event in he magma. Further east again, al the end of the zone, a north-trending breccia cuts the porphyritic gabbro and postdates mineralization. A porphyritic monzonite intrudes the porphyritic gabbro at the western end of the mineralized zone, and trenches in the vicinity of this intrusion give the best PGE values.
Saussuritization accompanies the mineralization, and occurs locally throughout the zone, particularly at the western end. Disseminated pyrrhotite, chalcopyrite, and pyrite occur as net textures around ferro-magnesian minerals, and in the veins associated with saussuritization, where PGE are present. Saussuritization gives the purple gabbros a bleached appearance. Local patches of magnetic melanogabbro to leucogabbro occur sporadically along the zone. At the eastern end of the mineralized zone, bands of magnetic clinopyroxenite, 2 to 50 cm thick, occur 50 m northwest of the breccia. These bands are not continuous along strike for more than 5 to 10 m, and may represent a fluidization event related to the breccia rather than primary layering. A unique 1 to 2 meter wide, north-trending, ultramafic dike cuts the western end of the zone and postdates mineralization. This, and another north-trending dike lo-cated on the southwestern side of Jock Lake, appear to have been intruded into pre-existing north-trending faults.
In summary, primary pyrrhotite and chalcopyrite appear to have been deposited in a linear zone near the margin of Davies' (1965) biotite-augite diorite, within a porphyritic gabbro phase. Late enrichment of this mineralization, accompanied by saussuritiza-tion, may be due to intrusion of the porphyritic monzonite. A similar environment for PGE's has been described in the Coryell alkalic intrusions in British Columbia (Hulbert et al. 1988). MacDonald and Cherry (1988) noted that the alkalic suite of' porphyry copper deposits has been shown to contain elevated PGE levels: a similar type of enrichment may have occurred at the Jock Lake Occurrence. |
