Abstract

The Jacinto vein system in the Camaguey district of central Cuba is a low-sulfidation, adularia-sericite epithermal gold deposit. It is hosted by volcanic and volcaniclastic rocks of Cretaceous age along the margin of the Camaguey batholith. Jacinto is unusually old and much more closely associated with a large batholith than would be expected for an epithermal vein deposit in an island arc. This study was undertaken to determine how Jacinto could have been preserved for so long. The Jacinto system includes at least five veins that range in length up to 1 km, have maximum widths of 60 m, and extend to depths of at least 150 m. The veins consist almost entirely of quartz, with minor amounts of adularia, calcite (commonly bladed), pyrite, and gold, which form at least 20 growth zones that can be divided into five main stages and can be correlated from one vein to another. Gold ore shoots are restricted vertically and are more continuous horizontally. Their present configuration suggests that the entire system has been tilted about 5 degrees to the northeast. Wall-rock alteration is limited and consists of minor K feldspar and sericite. Fluid inclusions in vein quartz homogenize at temperatures of 200 degrees to 320 degrees C and freeze at temperatures characteristic of salinities of about 0 to 1 wt percent NaCl equiv. The presence of bladed calcite and silica pseudomorphs after bladed calcite suggests that the hydrothermal fluids boiled. Stable isotope analyses of quartz, calcite, and inclusion fluids indicate that the veins were deposited by waters with delta 18 O and delta D values that range from values just above those of magmatic water to those typical of Cretaceous meteoric water. 40 Ar- 39 Ar analyses of adularia in the Jacinto veins indicate an age of about 72 Ma for mineralization, and geologic relationships suggest that the vein system is related to La Sierra rhyolite flows and domes of that approximate age. La Sierra rhyolite was extruded onto an erosion surface that exposed the Camaguey batholith and related volcanic rocks, indicating that erosion rates were relatively rapid immediately prior to formation of the deposit. Shortly after the deposit formed, however, it was tilted and then buried beneath Late Cretaceous to Eocene sediments of the Maraguan basin, which are being eroded to expose the system today. This fortuitous sequence of volcanism, batholith emplacement, rapid erosion to deep batholith levels, extrusion of rhyolite, and local sedimentation appears to be the result of collision between the Cuban arc and the Bahamas platform. Similar collisions between arcs and continental masses could have formed other epithermal deposits.

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