Epithermal gold mineralization in an old volcanic arc: The Jacinto deposit, Camaguey district, Cuba

The Jacinto vein system in the Camaguey district of central Cuba is a low-s ulfidation, adularia-sericite epithermal gold deposit. It is hosted by volc anic and volcaniclastic rocks of Cretaceous age along the margin of the Cam aguey batholith. Jacinto is unusually old and much more closely associated with a large batholith than would be expected for an epithermal vein deposi t in an island are. This study was undertaken to determine how Jacinto coul d 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 growt h zones that can be divided into five main stages and can be correlated fro m one vein to another. Cold ore shoots are restricted vertically and are mo re continuous horizontally Their present configuration suggests that the en tire system has been tilted about 5 degrees to the northeast. Wall-rock alt eration is limited and consists of minor K feldspar and sericite. Fluid inc lusions in vein quartz homogenize at temperatures of 200 degrees to 320 deg rees C and freeze at temperatures characteristic of salinities of about 0 t o 1 wt percent NaCl equiv. The presence of bladed calcite and silica pseudo morphs after bladed calcite suggests that the hydrothermal fluids boiled. S table isotope analyses of quartz, calcite, and inclusion fluids indicate th at the veins were deposited by waters with delta(18)O and delta D values th at range from values just above those of magmatic water to those typical of Cretaceous meteoric water. Ar-40-Ar-39 analyses of adularia in the jacinto veins indicate an age of ab out 72 Ma for mineralization, and geologic relationships suggest that the v ein system is related to La Sierra rhyolite flows and domes of that approxi mate age. La Sierra rhyolite was extruded onto an erosion surface that expo sed the Camaguey batholith and related volcanic rocks, indicating that eros ion rates were relatively rapid immediately prior to formation of the depos it. Shortly after the deposit formed, however, it was tilted and then burie d beneath Late Cretaceous to Eocene sediments of the Maraguan basin, which are being eroded to expose the system today. This fortuitous sequence of vo lcanism, batholith emplacement, rapid erosion to deep batholith levels, ext rusion of rhyolite, and local sedimentation appears to be the result of col lision between the Cuban are and the Bahamas plat form. Similar collisions between arcs and continental masses could have formed other epithermal depo sits.