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be very similar to the Abraham Creek body, of which it may be a part; and the intervening 3 square miles of Takla group rocks may be an isolated roof pendant. Compared with most of the Abraham Creek body, the body west of Mount Elsie is less complex, and consists essentially of a central band of hornblendite and appinite, intruded by dykes of various types of hornblende diorite, flanked by areas up to 4 mile wide of relatively uniform, medium- to coarse-grained hornblende diorite. Some of the hornblende in these rocks occurs as ragged green crystals and felted net- works of elongated prisms; it may represent alteration in place from pyroxene. A bluff overlooking Abraham Creek Valley includes a rock containing about 30 per cent hornblende in black, elongated, prismatic crystals up to 14 inches long, distributed with apparent random orientation in an interstitial groundmass of saussuritized plagioclase.

Tutizzt Lake Body

A body about 5 square miles in area northwest of Tutizzi Lake is composed of highly altered pyroxenite and diorite, cut by numerous diorite and feldspar porphyry dykes. About half the mass is of very basic or ultrabasic composition, and seems to have originally been mainly pyroxenite. The remainder of the body is diorite containing 30 to 60 per cent dark minerals.

The freshest pyroxenite is a dark olive-green to dull grey, mainly coarse, uniform-grained rock composed of augite crystals about 4 inch long. Small parts of this rock are relatively fine grained; and very coarse, pegmatitic varieties were not observed. The rock has been severely sheared and altered, and about half of it has been more or less completely changed to ragged, impure grains of uralitic amphibole. In other places the pyroxene has been reduced to an indefinite dark bluish grey material, which is seen in thin section to be a confused aggregate containing amphibole, carbonate, serpentine, epidote, magnetite, and much unidentifiable matter. Still other altered rocks appear to be mainly serpentine, with lesser fine-grained amphibole. One distinctive alteration product, found in many shear zones up to 50 feet wide, is a light grey or green tremolite rock composed of uralite largely to completely converted to a felted mass of fibrous tremolite. Semi-flexible fibres of tremolite up to 1 inch long were encountered, accom- panied in places by calcite, which also has a fibrous habit. Some of the pyroxenite has apparently suffered considerable movement during shearing, and fragments of subrounded, coherent, altered pyroxenite are embedded in wide bands of highly sheared altered pyroxenite.

The most abundant diorite is a moderately coarse-grained pyroxene diorite, consisting of about equal proportions of saussuritized feldspar and uralitized pyroxene. No rocks were found to contain feldspar sufficiently fresh to enable its composition to be determined. The diorite clearly intruded the altered pyroxenite, in which it is found as irregular fingers and dykes, with sharp contacts. Much of the diorite contains inclusions of uralitized pyroxenite and meladiorite. The diorite varies considerably in composition and texture from place to place within the body, but the different varieties grade irregularly into one another, and seem to be parts of a single, heterogeneous intrusion rather than representatives of a series of intrusions, each of slightly different composition.