Abstract A northerly trending zone of porphyry Cu-Au, porphyry Au, polymetallic replacement Pb-Zn-Au-Ag, and sedimentary rock-hosted Au deposits along the northwest margin of the Late Cretaceous Timok Magmatic Complex forms a part of the Bor metallogenic zone in eastern Serbia. The porphyry Cu-Au, epithermal quartz-alunite, and polymetallic replacement deposits in the northwest margin of the Complex represent parts of zoned magmatic-hydrothermal systems that are linked to Late Cretaceous oxidized, hornblende-biotite diorite porphyry intruded over a ~5- to 6-m.y. period between 83.6 ± 0.5 and 78.5 ± 1.3 Ma (U-Pb SHRIMP-RG ages on zircon), making them slightly younger than the larger Late Cretaceous (89-83 Ma) porphyry Cu-Au and high-sulfidation Cu-Au deposits in the eastern part of the Complex. The low-temperature sedimentary rock-hosted Au deposits in the northwest lie spatially near to, but are always separated by faults from, the polymetallic replacement and porphyry Cu-Au deposits. However, the common but not ubiquitous spatial association between the sedimentary rock-hosted Au deposits and the zoned porphyry Cu polymetallic replacement deposits, coupled with available exploration geochemical vectors evident in soil geochemistry, does suggest a genetic linkage between all the hydrothermal deposits. An important component required to fit the deposit types into a zoned magmatic hydrothermal model is a revised geologic and tectonic understanding that can also be extended to the entire Timok Magmatic Complex. A component of the revised model emphasizes the role of the Cenozoic faults formed during oroclinal bending of the region. Two fault generations are significant. Postmineral easterly trending normal faults bounding basins filled largely by early Miocene sedimentary rocks preserved the low-temperature sedimentary rock-hosted Au deposits and helped preserve deposits in the eastern area of the Complex. These faults accommodated elongation of the Complex and are kinematically linked to dextral strike-slip faults, such as the Timok-Cerna fault system, with as much as 100 km of displacement. Major, postmineral, NW-trending faults dismembered deposits in the northwest and accommodated sinistral displacement, which on a larger scale facilitated rotation between large crustal blocks, as well as Timok Magmatic Complex-scale shortening normal to the Complex during oroclinal bending of the region. The end result of the postmineral deformation during oroclinal bending and extensional and strike-slip deformation is preservation of different crustal levels, not just in the northwest but also throughout the region. The deformation furthermore enhanced the preservation of Cretaceous ore deposits beneath younger rocks. Because the Complex was constructed over a highly faulted Variscan and older basement terrane, it is possible that reactivation of the pre-Cretaceous basement faults in the basement beneath the Complex, such as the Variscan Blagojev-Kamen-Rudaria fault systems, played a role in the Late Cretaceous history of the Bor metallogenic zone, as well as controlling post-Cretaceous deformation in the Complex.

Abstract Porphyry Cu ± Mo ± Au deposits require the coincidence and positive interaction of a series of individually commonplace geological processes. They, and all their genetically associated deposits, are a natural consequence of convergent margin magmatism, and reflect the dynamic interplay between magmatic, hy-drothermal, and tectonic processes. Magmas generated during subduction rise into the upper crust, commonly along zones of lithospheric weakness, where they pond in tabular magma chambers at depths of 6 km or deeper. The chambers grow laterally by chamber floor depression (cantilever mechanism) and some roof lifting (piston mechanism). Apophyses rise from the parental magma chamber and intrude to within 1 to 3 km of the surface, where they may undergo volatile exsolution and crystallization as por-phyritic stocks. Emplacement of porphyry stocks is facilitated by structural anisotropy in the roof rocks. Ascending hydrothermal fluids exsolved from the porphyry stocks and the underlying parental magma chamber are focused into the cupola, taking advantage of vertical structural and rheological anisotropies introduced either before or during porphyry emplacement. From a structural standpoint, three recurrent processes enhance permeability in the form of fracture or breccia networks through which hydrothermal fluids pass and precipitate minerals. Fracture-producing events are related to intrusion of pre-, syn-, and post-mineral porphyry stocks or dikes to near-surface depths (1-3 km), phase separation and volume expansion of a hydrothermal fluid through a variety of mechanisms, and tectonically induced failure. Concentric and radial fracture patterns reflect magmatic processes whereas more linear arrays of veins reflect tectonic influences. The resulting different vein arrays are commonly vertically and temporally distributed in the porphyry system; concentric and radial arrays are more common above or in the upper parts of the stocks, whereas linear arrays dominate at depth, forming as the system cools and the pluton solidifies. Orthogonal and conjugate arrays of veins characterize all scales and all parts of porphyry systems. Veins from a particular paragenetic stage do not have unique orientations, but rather occur with all orientations typical of that system. The common conjugate to orthogonal inter-vein relationships in porphyry Cu deposits requires repetitive exchange of principal stress orientations, events that are facilitated by conditions of low differential horizontal stress. Such stress conditions indicate that many porphyry Cu deposits form in specific environments where the magmatic arc is under a near-neutral stress state. These conditions occur either in areas removed from active deformation, or during periods of stress relaxation and low strain in the magmatic arc. Achievement of these conditions in time and space is likely to be infrequent and transitory during the life of a convergent margin, which may explain the spatial and temporal clustering of deposits in large porphyry districts.

Abstract Within the central part of the Sulphur Creek Mining District six epithermal gold-mercury deposits have been mined, the West End, Central, Cherry Hill, Empire, Manzanita, and Wide Awake (Fig. 1). The mining district also includes the Abbott, Elgin and Rathburn mercury deposits and several hot springs that are depositing gold and cinnabar. The association of gold and mercury in the district was recognized early and gold was mined at the Cherry Hill and the Manzanita Mercury Mine from 1865 to 1891 with total production being about 3,000 oz of Au (Whitney, 1865, and Bradley, 1916). Whitney (1865) describes cobbles of cinnabar from the Sulphur Creek Mining District containing plumes of gold distributed through out the cinnabar. Fine placer gold is also present in drainages within the Sulphur Creek district, but has not been mined. Total mercury production from the district has been about 33,000 flasks, primarily from the Abbott mine. The Wide Awake mine was reported to have reserves of 24,000 flasks in 1899 and substantial unreported production may have come from this mine. In 1977, Homestake Mining Co. delineated a small gold deposit in the area of the Cherry Hill, West End, and Wide Awake Mines. The mineralization extends under the Sulphur Creek valley which separates these mines. Although numerous high-grade gold veins are present, typically greater than 0.3 oz of Au with multiple oz assays common, the veins are widely spaced and the deposit is presently uneconomic.