On genesis of massive sulfide polymetallic ore deposits of Rudny Altai

Many geologists assign most of large- and medium-sized massive sulfide polymetallic ore deposits of Eastern Kazakhstan to the VMS type. These ore deposits formed in the Devonian, under conditions of rifting and active basalt-andesite-rhyolite volcanism. Ore bodies of these deposits are noted to be clearly confined to formations of several geochronologic levels (D1e to D3fm). Hydrothermal-sedimentary syngenetic and hydrothermal-metasomatic ores are distinguished. High concentrations of base metals in the ores (above 10 % sum metals) and their rather simple mineral composition (chalcopyrite, pyrite, galena, and sphalerite) are a characteristic feature of all the massive sulfide polymetallic ore deposits of Rudny Altai. The ores are noted to be multicomponental, with elevated contents of the admixtures of precious metals and rare elements (Cd, Se, Bi, Te, Ta, W, etc.). Mineralogical investigations of the ores have demonstrated an intricate relationships of the major ore minerals (chalcopyrite, pyrite, sphalerite, galena) that exhibit several generations and different geochemical specialization. Minerals of Au, Ag, Te, Bi, and other elements are encountered as individual grains or microscopic inclusions and stringers in minerals of Cu, Pb, and Zn. A significant vertical range of the ore mineralization (more than 100 m), the complexity and long duration of the ore-forming processes, the clearly defined confinement of the ore mineralization to certain geochronologic levels, – all these allow us to suppose a possibility of discovery of new ore lodes or individual ore deposits within the already known ore fields of the Kazakhstan segment of Rudny Altai

Patterns of transparent spinel formation at Kukhilal deposit, south-western Pamir

Two groups of spinel crystals, holohedral and anhedral, were recognized at Kukhilal deposit. The latter are transparent raw crystals. It was found that anhedral transparent spinels formed due to reaction minerals (hydrotalcite and Mg chlorite) formation as envelopes between forsterite and spinel. These envelopes generated magals. They are viewed as bimetasomatic mineral associations produced in contacts of spinel and forsterite crystals. It was found that neogenic minerals (hydrotalcite, Mg chlorite, serpentine, brucite, etc.) preserved fragile spinel relics from Alpine orogenesis tectonic deformations due to their ductility. Transparent spinel was preserved in hydrotalcite-chlorite magal part. Magals are proposed to be regarded as jewelry spinel orebodies. Microprobe and X-ray structural analyses of spinel, forsterite, hydrotalcite, chlorite and serpentine are presented.

Vilyui-Markha interfluve of Yakutia: a region prospective for Cu-Ni-PGM mineralization

Materials are discussed on geologically similar structure of Norilsk ore district (NOD) and Vilyui-Markha interstream area (VMIA), which implies the latter prospects for Cu-Ni-PGM mineralization. Data is provided on Cu-Ni-Co-Zn mineral occurrences within Ygyattinsky diamondiferous region centered on VMIA. Geological similarities of NOD and VMIA are summarized below. Both regions are located in Mesozoic tectonomagmatic activation domain at the edge of large troughs: NOD is localized in the Siberian platform foredeep, and VMIA lies at Vilyui syneclise margin. NOD deposits are hosted by centroclines of large brachysynclines at slopes of Pyasinskoye dome. Within VMIA, prospects are located at Syuldyukarskoye dome slopes in margibal parts of large troughs. NOD and VMIA comprise Paleozoic marl-carbonate strata overlain by carbonaceous Carboniferous-Permian overburden, which could be assimilated by basaltic magma in Mesozoic contributing to its ore differentiation. Norilsk-Kharaelakh ore-bearing intrusion in VMIA appears to be similar to Kholomolokh sulfide-rich intrusion with its inferred extensive ore-bearing sills. They have similar composition and structure including presence of pegmatites. Ore-controlling Norilsk-Kharaelakh fault is believed to be simi- lar to Khatyryk-Kholomolokh fault, which was traced for 24 km by drilling and is one of sutures within deep-seated kimberlite-controlling Vilyui-Markha zone. This fault’s impact zone host concentrated geochemical anomalies and Cu-Ni-Co-Zn-Pt-Au-Ag Khomustakh occurrence. Based on this, Norilsk-type Cu-Ni prospects ranked as a potential ore cluster and three ore fields were identified

Buried Fe-Mn nodules on the World ocean floor

Ocean floor Fe-Mn nodule sequence is a product of Mesozoic-Cenozoic global epoch of Fe-Mn oxide ore accumulation. Buried nodules formed in Late Paleocene-Eocene, Late Cretaceous, Cenomanian.

Use of play analysis in ore deposit forecasting аnd prospecting

Play analysis was developed and is successfully used in oil and gas deposit prospecting. It is recommended for use in ore deposit forecasting and prospecting. Ore plays are deposits, mineral occurrences and prospects of common genesis, they are confined to a single structural and formational complex. Within one play, deposits are prospected and explored using the same technique; discovered deposits have similar technological ore properties. Geological/genetic and technological play uniformity simplifies their forecast assessment.

Specific features of postmagmatic and hypergene kimberlite rock alteration research

Methods of studying postmagmatic and hypergene kimberlite rock alteration, as well as identifying secondary minerals and their associations are characterized. It is shown that secondary mineral formation processes took place in a wide temperature range and they are caused by their downward change of medium reaction from alkaline to acidic followed by neutralization, which resulted in dissolution, additional growth and emergence of new secondary mineral generations.

The Oldoynio Lengai volcano, Tanzania: the essence of its recent eruptions

The article considers the nature of the volcanic fluxes that are traditionally interpreted as the only example of recent mantle-derived carbonatite lavas (carbonate magmas or melts) on the Earth. However, it turns out that this is not correct. These fluxes represent muddy soda masses with organics. Their source are masses of solutions and sediments of the Natron alkaline lake, that penetrate deep to the above-chamber space of the volcano along riftogenic faults, where they are heated and then erupt as fluxes, geysers, and ash masses. The eruption products in turn get to the lake again. At the recent stage of development, the Oldoynio Lengai volcano represents an epimagmatic phreatic hydrothermal recycling system.

Compositional peculiarities of the host rocks and ores of the Lazursky ore field, Zmeinogorsk ore region of the Rudny Altai minerogenic zone

The article describes composition of the host rocks and ores of the Lazursky and Maslyansky polymetallic volcanogenic massive sulfide deposits of the Lazursky ore field located within the Zmeinogorsk ore region of the Rudny Altai minerogenic zone. The ore field is composed of various facies of the Devonian (Late Givetian – Frasnian) ore-bearing siliceous-terrigenous basalt-rhyolite formation containing horizons of synvolcanic metasomatites. All rocks of the ore field were subjected to folding and schistosity with zones of tectonic brecciation. Hydrothermal alterations are represented by carbonatization and chloritization. The ore bodies exposed at the Lazursky and Maslyansky ore deposits are represented by copper-pyrite, copper, and zinc-copper-pyrite massive sulfide ores and other varieties. The major ore minerals of the deposits are chalcopyrite, pyrite, sphalerite, marcasite, and pyrrhotite.

Erguveem Ore Region in the eastern Chukotka Peninsula: An effect of the tectonics of the ore-bearing volcano-structures on composition of the gold-silver mineralization

The geological and structural position of the Pepenveem and Korrida Au-Ag ore occurrences situated in the East-Chukotka segment of the Okhotsk-Chukotka Volcanogenic Belt (OCVB) was studied. The Pepenveem ore occurrence was characterized by one (volcanogenic) mineralization stage. It is localized within a graben-like monocline composed of Late Cretaceous volcanics. A relatively stable tectonic regime caused rather low temperature and pressure gradients during the ore formation and, consequently, simple mineral composition of the ores and absence of advanced argillic alteration. In contrast, the Korrida ore occurrence was characterized by two (volcanogenic and plutonogenic) mineralization stages. It is localized within a plutonogenic uplift complicated by a regional fault zone. Here, the basement of the volcano-structure, composed of island-arc volcano-sedimentary rocks, was uplifted to the surface by numerous high-angle faults. The here observed extensive development of zoned metasomatic haloes (including advanced argillic alterations), abundance of mineral species, and sharp temperature and pressure gradients could resulted from tectonic activity in a zone of interaction between the plutonic dome and deep-seated regional fault.

Secondary dispersion haloes in the gold-bearing weathering crust of the Vasilkovskoe gold deposit, Northern Kazakhstan

The formation conditions and characteristics of secondary dispersion haloes in the gold-bearing weathering crust of a gold-sulfide-quartz deposit are considered. The fraction < 0,1mm is demonstrated to be preferable for lithochemical prospecting for the Vasilkovskoe type gold mineralization. The secondary dispersion haloes of gold, identified based on analyses of this fraction, are characterized by the maximum size and productivity.