Copper Deposits of Yukon and northern British Columbia

The Guichon Creek batholith (GCB), located in south‐central British Columbia, contains several large, low‐grade copper deposits of considerable economic importance. The surface geology of the Guichon batholith and its surrounding region have been well mapped; however, little information about subsurface features is available. The batholith consists of four major phases, emplaced radially outward, which can be separated on the basis of their texture and composition. Previous interpretation of gravity data suggests a mushroom‐shaped structure for the batholith. Data from Lithoprobe seismic reflection line 88-11, acquired across the batholith in 1988, reveal weakly coherent east‐dipping reflections on the west side and west‐dipping reflections on the east in the upper 10 km. To determine if these are related to structures associated with the batholith, we reprocessed the upper 6 s with particular emphasis on applications of signal enhancement techniques (e.g., pattern recognition methods, refraction statics, dip moveout corrections) and correlation of the improved subsurface images with the geological environment associated with porphyry copper deposits. Low near‐surface velocities correlate well with the phases of the batholith hosting the major copper deposits, which structurally lie in faulted and brecciated regions. Although the top 1.5 km cannot be imaged by the regional‐scale seismic reflection data, the reprocessed seismic section helps define the edges of the batholith, its various concentric phases, and the stem in the depth range of 1.5 to 10 km. The seismic results are complemented by 2.5-D (profile sense) modeling and 3-D inversion of regional‐scale gravity and high‐resolution aeromagnetic data. These show a low‐density and low‐magnetic‐susceptibility region associated with the batholith that extends to more than 10 km depth. The region of active mining interest lies above a circular low‐susceptibility area at 2 km depth and a low‐velocity region. Integrated interpretation of geophysical results and geological observations indicates the GCB is a funnel‐shaped feature in which mineralization is located above the stem of the batholith.

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The Origin of Sheet Fractures in the Galore Creek Copper Deposits, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e71-068 ◽

1971 ◽

Vol 8 (6) ◽

pp. 704-711 ◽

Cited By ~ 1

Author(s):

Donald G. Allen

Keyword(s):

British Columbia ◽

Hydrothermal Alteration ◽

Porphyry Copper ◽

Surface Feature ◽

Porphyry Copper Deposits ◽

Volume Increase ◽

Copper Deposits ◽

Feature Characteristic

A surface feature characteristic of the Galore Creek copper deposits is a set of well-developed closely-spaced fractures, termed sheet fractures. The formation of these fractures is attributed to the widespread presence of anhydrite, a hydrothermal alteration mineral associated with copper. The fractures apparently developed as a consequence of the volume increase due to hydration of the anhydrite to gypsum by meteoric water.The Galore Creek deposits have many characteristics of porphyry copper deposits, in many of which anhydrite or gypsum has been reported. Anhydrite may be responsible for the development of sheet fractures elsewhere.

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