anes

Sheitaicrelleniale yar ellen ieiavel nied arses PyROxenitg ge oes

‘+ Murray Ridge and Pinchi Mountain are formed of stocks of pyroxenite, each at least 15 square miles in area. A body of pyroxenite, about'a mile in diameter, is also exposed near the centre of the area of quartz diorite and diorite stock west of Indata Luke. This pyroxenite grades into gabbro and the gabbro, in turn, grades into the surrounding diorite and quartz dierite. The pyrexenites ar coarse-grained, dark green, reddish brown weathering rocks composed primarily of ‘pyroxene with small amounts of magnetite. They aro partly to completely altered to olive~ or emerald-green, antigorite serpentine. Small bodies of serpentine, each less than 2 square’ mile in area, are exposed on the south side of Pinchi Lake 3 miles from the east end; near the Pinchi Lake mercury mine; just east of Takatoot Lake; and on the east side of Indata Lake about a mile from the south end. They are so completely serpentinized and otherwiso altered that their original composition is mecertain. The small serpentine bodies and the rocks constituting the southern border of the Pinchi Mountain pyroxenite mass have been changed to buff-coloured carbonate-quartz- mariposite rocks.

Granodiorite, Quartz Diorite, and Related Rocks

The largest body of these rocks extends from Tchentlo Lake (second Nation Lake) north to Kwanika Creek and occupies an area of at least 200 square miles. A stock, approximately 5 square miles “in area, cuts Permian rocks west of Tsayta and Indata Lakes (third and fourth Nation Lakes). Medium- to coarse-grained, pink and light green granodiorite and quartz diorite are common, but grade into coarse-grained, darker green diorite, gabbro, and pyroxenite. The more basic rocks predominate in the border zone of the batholith cast of the Nation Lakes, and near the centre of the stock west of these lakes. ‘Small areas of similar granodiorite occur 1 mile west of Tachie River and 4 miles‘west of Tchentlo Lake. They. are parts of larger bodies to the west. Small stocks of fine- to medium=-grained, green diorite outcrop north of the Pinchi Lake sawmill and on the ‘south ‘side of Pinchi Lake opposite the mercury mine. In addition to “the intrusive rocks mapped are many aplitic and lamprophyric dykes up to 25 feet wide. These are associated principally with: larger intrusive bodies.

“The intrusive rocks cut Upper Triassic strata along Kwanika Creek.: They appear also to crosseut the Jurassic rocks, although no actual contacts were observed. Therefore, the period of ' their intrusion is’probably Jurassic or later. 3"

De . “a Conglomerate

At two localities on Kwanika Creek-and three localities “on or near Roddacker Creek outcrops of reddish brown conglomerate were observed. The conglomerate is made up of well-rounded pebbles and boulders ranging from a fraction of an inch to 18 inches diameter and embedded in a rusty red, arkosic matrix. They consist of pink and green quartz diorite and diorite, dark grey chert, black argillite, grey and buff arkose and greywacke, and white quartz and feldspar. All pebbles and boulders are coated with limonite and have glistening reddish brown surfaces. Beds of red-brown arkose a few feet thick occur with the. conglomerate on Roddacker Creek. The thickness of the conglomerate is unknown, but it exceeds 100 feet. The conglomerate on