Spatial and temporal evolution of fluids in hydrothermal ore deposits

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Virginia Tech


Magmatic-hydrothermal systems typically have vertical extents of several hundred
meters and their geochemical characteristics (e.g. mineral assemblages) vary considerably
over that vertical extent. As a consequence the expression in outcrop varies depending on
the level of erosion. Therefore understanding the geochemical zonation of magmatic-hydrothermal
ore deposits opens the possibility to detect deep magmatic-hydrothermal
systems, and to assess qualitatively the degree of erosion that has taken place in the area
and at which level the mineralization may occur. This dissertation presents the
characterization of two shallow hydrothermal systems and their potential relations with
deeper magmatic-hydrothermal systems. In addition, this dissertation develops the
equations to directly interpret thermometric data from the fluid inclusion type dominant in
one of those deposits (fluid inclusions that homogenize by halite disappearance).
Red Mountain, AZ is a porphyry copper system with a well-preserved lithocap
providing an ideal candidate to characterize the shallow expression of porphyry copper
systems in the southwestern US. The distribution of fluid inclusions, alteration mineralogy
and grade indicate that the intrusive responsible for the mineralization was only partially
intercepted during the exploration program and that one single magmatic event was likely
responsible for the mineralization detected. Fluid inclusion types and clay minerals are
systematically distributed within the deposit. The fluid responsible for the shallow
hypogene mineralization was a low pH-intermediate temperature-low density fluid while a
high salinity fluid was responsible for deep mineralization.
Wutong is a Pb-Zn-Ag deposit in the Nanling belt (southeast China). The combination
of fluid inclusion and mineral thermometry indicates that the Wutong deposit formed at
relatively low pressures. The age and isotopic composition of the mineralization indicates
that the deposit formed during the Cretaceous from crustal derived fluids. The occurrence
of a shallow magmatic-hydrothermal system of Cretaceous age in this region suggests that
Cretaceous intrusions, despite not outcropping very commonly in this particular region may
occur at deeper levels.



fluid inclusions, porphyry copper, Red Mountain, Arizona, alteration, mineralization, Cathaysia, Yanshanian, chalcopyrite disease