Abstract The Yerington district, Nevada, hosts at least four porphyry copper deposits and several small Fe oxide-copper-gold lodes within a middle Jurassic batholith and its volcanic cover. The contact aureole of the batholith contains early garnet-pyroxene hornfels and endoskarn, later copper-bearing andradite skarn deposits, and latest-stage large Fe oxide-copper-gold replacement deposits. The Jurassic host rocks have been faulted and tilted 60° to 90° W by Cenozoic normal faulting ( Proffett, 1977 ) so that the modern exposures represent cross sections of a complex paleohydrothermal system from the volcanic environment to about 7 km depth. This paper summarizes field, petrologic, and geochemical data that support the origin of hydrothermal wall-rock alteration and ore deposition due to two different types of fluids. Magmatic brines were derived from the crystallization of the youngest equigranular intrusion of the Yerington batholith, the Luhr Hill granite. Brines separated from the granite and were emplaced upward together with granite porphyry dikes to produce copper-iron sulfdes and associated K silicate alteration in the porphyry copper deposits and copper skarns. In the upper part of the hydrothermal system, magmatic fluids are an important source of acids and sulfur that produced sericitic and advanced argillic alteration. A second type of ore fluid is brine derived from formation waters trapped in the Triassic-Jurassic sedimentary section intruded by the batholith. These fluids were heated by the batholith and circulated through its crystalline parts. Hornfels and endoskarn were produced along the contact of an early intrusion. Following intrusion of the porphyry dikes, sedimentary brines circulated up to 3 km into the batholith and upon heating produced sodic-calcic alteration there. Ascent of these brines, particularly after the waning of magmatic fluid input, may have caused shallow-level chlorite-dominated alteration in igneous host rocks and Fe oxide-Cu-Au lodes and replacement deposits in the batholith and its contact aureole, respectively.

Abstract The Elatsite porphyry copper deposit is situated 6 km south of the town of Etropole, in the northern part of the Panaguyrishte-Etropole ore region (Figs. 1 , 2 ) as part of the Elatsite-Chelopech ore field (Appendix 2, 5). The deposit is located about 10 km NW of the Chelopech volcanic center. It is emplaced along the contacts of Upper Cretaceous dykes (porphyry granodiorite, quartz dioritic or monzo-syenodiorite) with the Precambrian-Cambrian phyllites (Figs. 2 , 3 ; Appendix 5). The phyllites are contact- metamorphosed to hornfels adjacent to the dykes and Paleozoic granodiorite. The dykes dip to the south toward the magma chamber of the volcano-intrusive structure (Fig. 4 ). Porphyry Cu-Au-PGE mineralisation (Re/Os age 92–92.4 Ma; Zimmerman et al., 2003 ) is genetically connected to Late Cretaceous subvolcanic intrusions of quartz-monzonitic to granodioritic composition (U/Pb age 91.5–92 Ma; von Quadt et al., 2002 ), but it is also hosted in Paleozoic granodiorites (314 Ma; von Quadt et al., 2002 ) and in greenschists. The porphyry ore stock has a lens-like shape elongated to the NE, and it dips at 40°–50° to the South; it is 1,300 m long and 200 to 700 m wide. At depth the ore- body was traced more than 550 m. The porphyry- copper, Mo, Au and PGE mineralisation is hosted mainly in the granodiorites, but it is also abundant in porphyry dykes of quartz syenodiorite (Figs. 5 , 6 ) and is best developed

Abstract The close spatial and temporal association between intermediate to felsic igneous intrusions and large tonnage, low-grade porphyry-type mineral deposits in arc environments is consistent with the hypothesis that magmas were the dominant source of the ore metals. In this paper , we review some aspects of the origin and emplacement of porphyry ore-related magmas, the controls on the magmatic concentration of ore metals, water , chlorine, sulfur, and related elements, and the factors that affect the partitioning of metals in magmatic-hydrothermal systems. The intermediate to felsic igneous rocks associated with ore are the end product of magmatic evolution that begins with the generation of mantle-derived arc magmas. High-alumina basalt is generated by the complex interaction of fluids released from subducting slabs and the overlying mantle wedge. Fluids released early from the slab may be higher in chlorine, as well as in related volatile and fluid-soluble elements. Fugacities of oxygen and sulfurous gases in arc magma systems may be controlled in part by sulfate-oxide-sulfide assemblages in the subducting plate. Water, chlorine, and sulfur may be sourced partially from seawater by way of subducted oceanic lithosphere. Ore metals in arc magmas probably have diverse origins, including the mantle wedge, the lower continental crust, and the subducted lithosphere. Dilational tectonic features may accommodate some high-level plutons, as well as their associated cupolas and apophyses. The large-scale through-going fractures that host these local zones of dilation can extend to lower crustal depths and thereby facilitate the movement of magma from depth. The structures that represent zones of crustal weakness below the magma chamber and that promote magma ascent also provide regions of weakness above the chamber and promote the formation of cupolas, apophyses, and zones of high vein density. During the growth of plutonic complexes, active magma chambers may be smaller than the developing plutonic complex at any given time. Significant devolatilization may occur upon magma rise, with ore zones located above the root-feeder zone of the chamber. Volatile-melt-crystal interactions are important at all structural levels in the crust, and may be quite important in controlling not only the water, sulfur, and chlorine concentrations but also the metal concentrations in the epizonal magmas that generate porphyry ore deposits. Generally, the formation of magmatic-hydrothermal deposits of chalcophile metals is favored by magmatic characteristics such as high Cl/H 2 O ratio, and early volatile exsolution relative to crystallization progress. The oxidation state of the magma is probably important in producing variations in ore-metal ratios in magmatic-hydrothermal ore deposits.