Abstract The basal parts of the Higher Himalayan Crystallines (HHC), Lesser Himalayan sedimentary sequences and mylonite zone at the base of Main Central Thrust (MCT) within the NW Himalaya clearly demonstrate anorogenic magmatic signatures at around 1860 Ma, as indicated by SHRIMP U–Pb zircon ages from Bandal granitoids, Kulu–Bajura mylonite and Wangtu granitoids along the Sutlej Valley, Himachal Pradesh. Some of the zircon crystals contain older cores mostly extending back to 2600 Ma. We report for the first time a 3000 Ma old zircon core from Wangtu granitoids, which indicates reworking of ensialic Archaean crust during the assembly of the Columbia Supercontinent between 2.1 and 1.8 Ga. During the Himalayan collisional tectonics, the reworked Archaean and Palaeoproterozoic crust was imbricated and placed adjacent to each other in the Higher Himalayan Crystallines, the Inner Lesser Himalayan window zone and the Kulu–Bajura Nappe.

Abstract The Yilgarn block is a major metallogenic province, currently enjoying its highest ever annual gold production from greenstone-hosted Archean mesothermal gold deposits. Gold mineralization occurs in ca. 2.95 to 2.7-Ga greenstone belts throughout the block, with over 2,000 deposits known, but is best developed in the ca. 2.7-Ga greenstones of the Norseman-Wiluna belt. Most mineralization is sited in brittle-ductile structures, at or below the amphibolite-greenschist transition, commonly in rocks with high Fe/(Fe + Mg) ratios. Sulfidation, K-(± Na-) metasomatism and carbonation are important alteration styles associated with such mineralization in shear zones, quartz veins, and/or breccias. Gold occurs most commonly within Fe sulfides and mineralization has a typical element association of Au-Ag-As-W±Sb±Te±B with low Pb-Zn-Cu contents. Gold was deposited from reduced to slightly oxidized, near-neutral, moderate-density, low-salinity H 2 O-CO 2 fluids at 250° to 350°C and 0.5 to 2 kbars in response to sulfidation and/or oxidation-reduction reactions, changes in pH, and pressure decrease over a limited temperature range. On the regional scale, the distribution of gold deposits is controlled by kilometer-scale, oblique-slip, reverse or normal faults-shears linked to crustal-scale, largely strike-slip, shear zones that also appear to control the distribution of mantle-derived carbonation and the emplacement of I- and A-type granitoids, felsic porphyries, and/or calc-alkaline lamprophyres. These associations, combined with radiogenic and stable isotope data, suggest that gold mineralization was related to fluid flow on a crustal or even lithospheric scale, rather than simply being related to greenstone belt devolatilization or local magmatic intrusions; lamprophyres do, however, represent a potential gold donor to the metamorphic-hydrothermal systems. Despite this gross control, the provinciality of isotope data suggests that ore components were strongly influenced by upper crustal fluid pathways, probably controlled by transient fluid flow into brittle-ductile structures under the influence of fluid-pressure gradients. The preferred model is that gold mineralization was the result of high lithospheric heat and fluid flux during compressional, oblique-slip deformation and mantle to crustal magmatism related to closure of the partly sialic-floored, marine basin now represented by the Norseman-Wiluna belt. As such, it shows similarities to Phanerozoic gold provinces in convergent-margin tectonic settings.

Abstract Certain aspects of the genesis of Archean epigenetic gold deposits remain controversial, in particular the source of the auriferous fluids, which are arguably magmatic, metamorphic, or mantle derived. In an attempt to constrain the fluid source, it is essential to consider Archean gold mineralization in terms of the tectonic, magmatic, and metamorphic history of greenstone terranes. Asymmetries in the distribution of volcanic, sedimentary, and plutonic rock types, the pattern of deformation, and the rapid evolution of the greenstone sequences within the Norseman-Wiluna belt in the eastern Yilgarn block are akin to those of younger orogenic belts at obliquely convergent continental plate boundaries. Archean gold deposits show many similarities to younger, cordilleran-style gold deposits (e.g., the Mother Lode) which occur in a similar tectonic setting, particularly in terms of their strong dependence on structural controls and the composition of the ore fluids. In the eastern Yilgarn block there is a coincidence of lode gold mineralization, calc-alkaline porphyry, and lamprophyre dike swarms and craton-scale oblique-slip faults with their attendent mantle-derived carbonation. With no compelling evidence for direct derivation of ore fluids from felsic magmas, gold mineralization is best viewed as the upper crustal expression of a deep-seated tectono-thermal event with mantle-crustal outgassing, occurring in response to a deep mantle heat source, related to convergent tectonics. In all probability the ore fluid contained magmatic, metamorphic, and mantle components, but it is impossible at this stage to determine with which component the gold was predominantly associated.