NOVEL "INTERSTITIAL QUARTZ VEINS" IN SILICIFIED CARBONATES OF A DETACHMENT FAULT, WHITE PINE RANGE, NYE COUNTY, NEVADA; IMPLICATIONS

A stacked, coalescing system of detachment faults in east-central Nevada contains a carbonate-hosted population of unusual quartz veins that did not originate by filling, enlarging, or replacing a fracture or similar pre-existing tabular structure. Rather, these veins consist of quartz crystals that nucleated in pore spaces of the primary carbonate matrix, then grew to engulf the surrounding matrix. Networks of such crystals form veins. These “interstitial quartz veins” could have formed in zones of divergent primary or diagenetic properties unrelated to brecciation or faulting, such as mineral content or permeability; as such they may have novel implications for recent studies of ore genesis as well as for the potential effect of silica veins on earthquake magnitude and frequency.

The Currant Gap detachment (CGD), part of a major fault system in Paleozoic rocks of east-central Nevada, is marked by a 40m-thick fault-bounded zone of massive, almost completely silicified limestone (called by us “SC-rock”) in a cliff face and erosional remnants elsewhere. Quartz and carbonate veins occur in carbonate rocks above and below the detachment. SC-rocks in the fault zone and adjacent carbonates were thin sectioned and subjected to acid dissolution; silica residues were analyzed by light microscopy and scanning electron microscopy (SEM).

Elongated, euhedral quartz crystals contain thousands of 5-20 mm carbonate inclusions, similar to grains in the surrounding matrix. Some crystals have inclusions to their boundaries, while others have a hexagonal-shaped “matrix core” of densely-packed inclusions, surrounded by an outer zone of clear quartz. SEM images show quartz crystals riddled with cavities, from which carbonate grains had been dissolved. Vein walls consist of the same euhedral quartz crystals of varying sizes, with a few gaps that would have contained carbonate. Completely silicified SC-rocks have elongated crystals (embayed because they are intergrown with other quartz crystals) with matrix cores, indicating that this type of vein played a major role in silicification along the CGD. Other types of silicification also occur, such as vug fillings and gel-front material. Our observations suggest a complex history of brecciation, faulting and silicification, with a wide temperature range (~100^o - <350^o).