| Abstract |
- The Bethlehem Copper Mine, a porphyry copper deposit, is
situated near the geographical center of the Guichon Creek batholith.
The Guichon Creek batholith is located on the east flank of the
Canadian Coast Range in south central British Columbia approximately
250 miles northeast of Vancouver, B. C. The batholith
trends northerly, is 40 miles long, 16 miles wide and divided in half
by a broad easterly trending saddle, the Highland Valley. Moreover,
it is composite and consists of two principal phases, an older quartz
diorite and a younger granodiorite.
The Bethlehem copper deposit is situated on the contact between
these two phases. Seven igneous rock types and several
breccia bodies have been recognized. The Guichon quartz diorite,
Early Jurassic in age, has been intruded by Bethlehem quartz
diorite, leucocratic porphyritic dacite, granite, granodiorite, dacite
porphyry, and mesocratic porphyritic dacite. The Bethlehem
quartz diorite is thought to be a marginal or cupola phase of the
granodiorite. Dacite porphyry, granodiorite, mesocratic porphyritic
dacite and possibly leucocratic porphyritic dacite occur as dike
rocks. The breccia bodies are believed to be related to the emplacement
of Bethlehem quartz diorite and leucocratic porphyritic
dacite with coincident or later explosive events.
Mining operations in the Jersey pit have exposed Guichon
quartz diorite, Bethlehem quartz diorite, dacite porphyry and
breccia. Bethlehem quartz diorite and breccia nearly circumscribe
a huge block of Guichon quartz diorite some 700 feet in diameter.
All rocks in the pit have been faulted, fractured, mineralized and
hydrothermally altered.
Faults consist of a northerly trending, west dipping essentially
parallel set. Obvious fractures are related to faults while the more
significant, indistinct, and randomly orientated hairline fractures
that control mineralization apparently are not.
Chalcopyrite, bornite and other metallic minerals occur as
scattered grains on fracture surfaces or less commonly as disseminations
replacing secondary mafics. The degree and extent of
mineralization is a function of permeability produced by fracturing.
Hydrothermal alteration associated with the Jersey pit is of both the propylitic and argillic types. Propylitic alteration fringes
and Jersey ore body and is characterized by the development of
epidote and chlorite at the expense of primary hornblende, biotite,
and less commonly plagioclase. Argillic alteration is restricted to
the central area of the pit, as is most of the significant mineralization
and is characterized by strong lime leaching and the development
of fine grained, but optically unresolvable, minerals believed
to be one or more types of clay minerals.
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