eGe

schists, and serpentines to quartz-carbonate-mariposito (greon miea)
rocks. The alteration consists mainly of the replacement of all
original minerals, except quartz, with ankeritic carbonates; as o ree
sult limestones and serpentine rocks show the most complete replace-
ment and quartzose rocks the least. Carbonatization preceded the
period of cinnabar mineralization along the Pinchi fault zone and
both processes were facilitated by the chauneiwey provided by the
faulting.

ECONOMIC GEOLOGY
Cinnabar Deposits

Cinnabar occurs at many places within the moetnenn part of the
Pinchi Lake mercury belt, but the only known deposits of workobvle size
and grade are those of Bralorne Takla mercury mine. ‘The deposits oocur
in rocks of quite different character, and all have been found in
crushed rocks of; or related to, the Pinchi fault’ zone.’

The cinnabar deposits may be classified on the basis of assooi-~

ated rocks as follows: (1) limestone type; (2) serpentine type; (3) other

types »

Limestone Type. The principal cinnabar deposits are found in
brecciated fault zones in Pormian limestone. Solution cavities, ranging
in size from mere pits to openings’ several feet across and partly filled
with calcite, are common in the limestone. The cinnabar occurs as vein-
lets, blebs, and individual grains filling pre-existing openings such
as fissures; solution cavities, and interstices between grains and
breccia. fragments. -Most of the cinnabar is the red, massive variety .
‘that weathers purplish red. “Some bright red, earthy, "paint" variety
films fracture surfaces in-the ore-bodies, It occurs mainly near the _
surface. Scattered grains of pyrite are found in most deposits. The
common gangue minerals are quartz and calcite. Quartz and cinnabar
seem to have been deposited contemporaneously, and the calcite both
earlier and later. Most of the quartz is fine-grained, but crystals
have also formed in open cavities. The amount of quartz varies greatly
from one deposit to another; in the deposits of the Bralorne Takla mer-
cury mine it is only a minor constituent. There has been some replacee
ment of limestone by cinnabar, especially along minute fractures in the
rock. In solution cavities, on the other hand, cinnabar forms on the
faces and cleavage planes of calcite crystals, and shows no evidence
of replacement. In general the relative amount of limestone replace-
ment by cinnabar varies indirectly with the size of pre-existing open-
ings, the smaller the openings the greater the proportion of replaced
wall+rock. Replacement, however, is not en important factor in the
grade of the ore, and the best ore occurs in limestone that contains
the greatest percentage of openings available for cinnabar SD SENS,

Serpentine Type. Cinnabar deposits ere commonly associated with
small, sill-like bodies of serpentine rock. Zones of shearing and brecci-
ation along the contacts of many of these bodies have provided channel-
ways for hydrothermal solutions. At an early stage this has resulted
in extensive carbonatization of the fractured rocks, in which process.
much of the serpentine has been replaced by quartz and chalcedony, an-
keritic carbonate, and mariposite, in widely varying proportions. At
& later stage, following further brecciation, mineralizing solutions
deposited cinnabar and chalcedonic quartz in the carbonatized and frac-
tured rocks. The cinnabar and chalcedony occur in minute veinlets
filling the fractures and coating the breccia fragments.’ No replace-
ment of the wall+rock is evident, and no other metallic minerals were
observed. The cinnabar-chalcedony veinlets sre cut by calcite stringers.
In many places it is difficult to SR ue a ee carbonates and silica
formed at various PueeCss