MAGNETIC PROPERTIES OF LATE CRETACEOUS-CENOZOIC VOLCANIC ROCKS OF THE SOVIET FAR EAST SOUTH

AbstractThe Tokoro Belt exposed in NE Hokkaido (Japan) represents part of a Late Cretaceous accretionary complex, which includes variously metamorphosed volcanic rocks that are interbedded with chert, lenticular limestone and some fore-arc sedimentary rocks. The Tokoro Belt is notably different from other Late Cretaceous accretionary complexes around the Pacific Rim because of widespread occurrence of basalts and volcaniclastic rocks in it. The Nikoro Group, characterized by widespread occurrence of volcanic rocks, is divided into western, eastern and southern sections based on the internal structure, geochemical affinities and metamorphic grades of their volcanic lithologies. OIB (ocean island basalt)-type volcanic rocks with low-grade metamorphic overprint predominate in the western and southern sections, whereas MORB (mid-ocean ridge basalt)- and OIA (ocean island alkaline basalt)-type rocks in the eastern section with partly high-pressure metamorphism make up the northern part of the eastern section. Trace element patterns display transitional trends from MORB to OIA geochemical affinities. OIB-type rocks display trace element characteristics similar to those of shield volcano lavas on Hawaii, rather than small and mainly alkaline, Polynesian hotspot lavas; furthermore, they show significant HREE (heavy rare earth element) enrichment probably caused by plume–ridge interaction. Widespread OIBs in the Tokoro Belt represents tectonic slices of a large (>80 km wide) Hawaiian-style, seamount shield volcano on the Izanagi oceanic plate that was accreted into the continental margin of Far East Asia in the Late Cretaceous.

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Gold in Mineralized Volcanic Systems from the Lesser Khingan Range (Russian Far East): Textural Types, Composition and Possible Origins

Geosciences ◽

10.3390/geosciences11020103 ◽

2021 ◽

Vol 11 (2) ◽

pp. 103

Author(s):

Nikolai Berdnikov ◽

Victor Nevstruev ◽

Pavel Kepezhinskas ◽

Ivan Astapov ◽

Natalia Konovalova

Keyword(s):

Iron Oxide ◽

Subduction Zones ◽

Gold Mineralization ◽

Russian Far East ◽

Far East ◽

Volcanic Rocks ◽

Liquid Immiscibility ◽

Explosive Volcanism ◽

Deep Roots ◽

Scientific Debate

While gold partitioning into hydrothermal fluids responsible for the formation of porphyry and epithermal deposits is currently well understood, its behavior during the differentiation of metal-rich silicate melts is still subject of an intense scientific debate. Typically, gold is scavenged into sulfides during crustal fractionation of sulfur-rich mafic to intermediate magmas and development of native forms and alloys of this important precious metal in igneous rocks and associated ores are still poorly documented. We present new data on gold (Cu-Ag-Au, Ni-Cu-Zn-Ag-Au, Ti-Cu-Ag-Au, Ag-Au) alloys from iron oxide deposits in the Lesser Khingan Range (LKR) of the Russian Far East. Gold alloy particles are from 10 to 100 µm in size and irregular to spherical in shape. Gold spherules were formed through silicate-metal liquid immiscibility and then injected into fissures surrounding the ascending melt column, or emplaced through a volcanic eruption. Presence of globular (occasionally with meniscus-like textures) Cu-O micro-inclusions in Cu-Ag-Au spherules confirms their crystallization from a metal melt via extremely fast cooling. Irregularly shaped Cu-Ag-Au particles were formed through hydrothermal alteration of gold-bearing volcanic rocks and ores. Association of primarily liquid Cu-Ag-Au spherules with iron-oxide mineralization in the LKR indicates possible involvement of silicate-metallic immiscibility and explosive volcanism in the formation of the Andean-type iron oxide gold-copper (IOCG) and related copper-gold porphyry deposits in the deeper parts of sub-volcanic epithermal systems. Thus, formation of gold alloys in deep roots of arc volcanoes may serve as a precursor and an exploration guide for high-grade epithermal gold mineralization at shallow structural levels of hydrothermal-volcanic environments in subduction zones.

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Accessory mineralization of rocks from Late Cretaceous intrusive series with Li–F granites in the Far East

Geology of Ore Deposits ◽

10.1134/s1075701515070028 ◽

2015 ◽

Vol 57 (7) ◽

pp. 537-551 ◽

Cited By ~ 3

Author(s):

V. I. Alekseev ◽

Yu. B. Marin

Keyword(s):

Late Cretaceous ◽

Far East ◽

The Far East

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Zircon U-Pb and fission-track ages of Late Cretaceous volcanic rocks of the Ieshima Islands, southwest Japan

Japanese Magazine of Mineralogical and Petrological Sciences ◽

10.2465/gkk.150622 ◽

2016 ◽

Vol 45 (2) ◽

pp. 53-61 ◽

Cited By ~ 5

Author(s):

Daisuke SATO

Keyword(s):

Late Cretaceous ◽

Fission Track ◽

Volcanic Rocks ◽

Southwest Japan ◽

Fission Track Ages

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Geochemistry, geochronology, and fluid inclusion study of the Late Cretaceous Newton epithermal gold deposit, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2015-0068 ◽

2016 ◽

Vol 53 (1) ◽

pp. 10-33 ◽

Cited By ~ 7

Author(s):

Lijuan Liu ◽

Jeremy P. Richards ◽

S. Andrew DuFrane ◽

Mark Rebagliati

Keyword(s):

British Columbia ◽

Gold Deposit ◽

Late Cretaceous ◽

Gold Mineralization ◽

Volcanic Rocks ◽

Fluid Inclusion Study ◽

Epithermal Gold ◽

Epithermal Gold Deposit ◽

Felsic Volcanic ◽

Felsic Volcanic Rocks

Newton is an intermediate-sulfidation epithermal gold deposit related to Late Cretaceous continental-arc magmatism in south-central British Columbia. Disseminated gold mineralization occurs in quartz–sericite-altered Late Cretaceous felsic volcanic rocks, and feldspar–quartz–hornblende porphyry and quartz–feldspar porphyry intrusions. The mineralization can be divided into three stages: (1) disseminated pyrite with microscopic gold inclusions, and sparse quartz–pyrite ± molybdenite veins; (2) disseminated marcasite with microscopic gold inclusions and minor base-metal sulfides; and (3) polymetallic veins of pyrite–chalcopyrite–sphalerite–arsenopyrite. Re–Os dating of molybdenite from a stage 1 vein yielded an age of 72.1 ± 0.3 Ma (published by McClenaghan in 2013). The age of the host rocks has been constrained by U–Pb dating of zircon: Late Cretaceous felsic volcanic rocks, 72.1 ± 0.6 Ma (Amarc Resources Ltd., unpublished data, reported by McClenaghan in 2013); feldspar–quartz–hornblende porphyry, 72.1 ± 0.5 Ma; quartz–feldspar porphyry, 70.9 ± 0.5 Ma (Amarc Resources Ltd., unpublished data, reported by McClenaghan in 2013). The mineralized rocks are intruded by a barren diorite, with an age of 69.3 ± 0.4 Ma. Fluid inclusions in quartz–pyrite ± molybdenite ± gold veins yielded an average homogenization temperature of 313 ± 51 °C (number of samples, n = 82) and salinity of 4.8 ± 0.9 wt.% NaCl equiv. (n = 46), suggesting that a relatively hot and saline fluid likely of magmatic origin was responsible for the first stage of mineralization. Some evidence for boiling was also observed in the veins. However, the bulk of the gold mineralization occurs as disseminations in the wall rocks, suggesting that wall-rock reactions were the main control on ore deposition.

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