Skip to Main Content
Book Chapter

Geology of the Bingham Canyon Porphyry Cu-Mo-Au Deposit, Utah

By
John P. Porter
John P. Porter
27 West Hill Park, Highgate Village, London N6 6ND, England
Search for other works by this author on:
Kim Schroeder
Kim Schroeder
27 West Hill Park, Highgate Village, London N6 6ND, England
Search for other works by this author on:
Gerry Austin
Gerry Austin
Search for other works by this author on:
Published:
January 01, 2012

Abstract

The Bingham Canyon porphyry Cu-Mo-Au deposit is located in the central part of the Oquirrh Mountains, 30 km southwest of Salt Lake City, Utah. The Cu-Au-Mo deposit lies at the center of a large polymetallic district, which includes proximal Pb-Zn-Ag replacement and distal sediment-hosted gold mineralization. Open-pit copper mining commenced in 1906 and through 2011 has produced 2.666 billion tonnes of ore averaging 0.74% Cu, 0.035% Mo, 0.448 g/t Au, and 3.29 g/t Ag.

Bingham lies near the west end of an 80-km-long belt of petrochemically similar Eocene to Oligocene intrusions and coeval volcanic rocks, which host base and precious mining districts. The Bingham district is centered on the Bingham stock, a multiphase mid-Eocene intrusion emplaced into a thick succession of folded mid- to upper Paleozoic siliciclastic and carbonate rocks. The 2 × 2 km Bingham stock consists mainly of premineral equigranular monzonite that was intruded successively by a 2-km-long dike-like body of quartz monzonite porphyry (QMP), long narrow dikes and sills of intramineral latite porphyry (LP), and narrower dikes of late-mineral quartz latite porphyry (QLP). The intrusions and associated porphyry-style mineralization dip steeply to the northwest and persist from the pre-mine surface at 2,390 m to below sea level. U-Pb zircon dating indicates a 38.6 Ma age for the equigranular monzonite and suggests that the subsequent porphyry intrusions were emplaced at ∼ 38 Ma. Porphyry intrusion and mineralization were approximately synchronous.

Early actinolite-stable alteration in igneous and sedimentary rocks is flanked by distal chlorite-epidote alteration. Magnetite-destructive secondary biotite alteration is pervasive in intrusive rocks that contain > 0.7% copper but typically is fracture-controlled and overprints earlier actinolite alteration in lower grade intrusive rocks and quartzites. K-feldspar alteration accompanies the highest grade copper and gold mineralization. Sericitic alteration is locally pervasive but, more typically, it is restricted to the margins of late quartz-pyrite veins. Late, low-temperature montmorillonite ± kaolinite alteration is ubiquitous in the intramineral porphyries and adjacent equigranular monzonite.

An outer zone of 0.35 to > 0.70% Cu mineralization surrounds and overlaps an inner zone of 0.05 to > 0.15% Mo mineralization, which in turn forms a cupola around a barren core. Intense bornite-chalcopyrite-chalcocite-gold mineralization (> 0.7% Cu and > 1 g/t Au) occurred directly above the barren core but has largely been removed by mining. The copper mineralization in the flanks of the deposit is dominated by chalcopyrite. Copper and gold grades decrease downward but quartz-molybdenite stockwork mineralization grading > 0.05% Mo extends to the lower limit of drilling. Equigranular monzonite is the predominant ore host, containing 53% of the ore mined to date.

Vein types proceed in a sequence from early biotite through quartz-sulfide to late anhydrite and zeolite. Early copper-bearing quartz veins are truncated by the LP and QLP dikes, but later copper-bearing veins cut the dikes. Cathode luminescence studies indicate that copper-bearing sulfides were deposited within micro-fractures and vugs created by dissolution of earlier quartz. Quartz-molybdenite veins postdate the copper-bearing veins and cut all of the porphyries. Vein densities reach > 10 vol % in the barren core and decrease to ∼ 1 vol % at the outer boundary of the > 0.35% Cu zone.

Published fluid inclusion and vein density studies, together with modeled grade distributions, show that mineralization was precipitated by a plume of metal-bearing fluid approximately 2 km in diameter, centered near the southeastern edge of the QMP. The barren core apparently represents an upflow zone near the top of which supercritical fluids separated into vapor and brine. Copper-bearing sulfides and gold precipitated as vapor-dominant fluids cooled from 430° to 350°C. Inclusions in quartz from the deep flanks of the copper deposit indicate similar fluid compositions, but less separation into vapor and brine.

You do not currently have access to this article.

Figures & Tables

Contents

Special Publications of the Society of Economic Geologists

Geology and Genesis of Major Copper Deposits and Districts of the World: A Tribute to Richard H. Sillitoe

Jeffrey W. Hedenquist
Jeffrey W. Hedenquist
Search for other works by this author on:
Michael Harris
Michael Harris
Search for other works by this author on:
Francisco Camus
Francisco Camus
Search for other works by this author on:
Society of Economic Geologists
Volume
16
ISBN electronic:
9781629490410
Publication date:
January 01, 2012

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal