TY - JOUR

T1 - Formation of au-bearing antigorite serpentinites and magnetite ores at the massif of ophiolite ultramafic rocks

T2 - Thermodynamic modeling

AU - Murzin, Valery

AU - Chudnenko, Konstantin

AU - Palyanova, Galina

AU - Varlamov, Dmitry

PY - 2019/12

Y1 - 2019/12

N2 - We constructed thermodynamic models of the formation of two types of gold-ore mineralization at the Kagan ultramafic massif in the Southern Urals (Russia). The first type of gold-mineralization is widely spread at the massif in the tectonic zones of schistose serpentinites containing typically ≤ 0.1 ppm Au. The second type of gold-ore mineralization is represented by veined massive, streaky and impregnated magnetite ores in contact with serpentinites. It contains to 5 vol.% sulfides and 0.2–1.2 ppm Au. Our thermodynamic calculations explain the formation of two types of gold-ore mineralization in the bedrocks of ultramafic massifs. Metamorphic water, which is the result of the dehydration of early serpentinites (middle Riphean) during high-temperature regional metamorphism (700 °C, 10 kbar) (late Precambrian), is considered as the source of ore-bearing fluid in the models. The metasomatic interaction of metamorphic fluid with serpentinites is responsible for the gold-poor mineralization of the 1st type at T = 450–250 °C and P = 2.5–0.5 kbar. The hydrothermal gold-rich mineralization of the 2nd type was formed during mixing of metamorphic and meteoric fluids at T = 500–400 °C and P = 2–3 kbar and discharge of mixed fluid in the open space of cracks in serpentinites. The model calculations showed that the dominant forms of gold transport in fluids with pH = 3–5 are AuCl2− complexes (≥450 °C) and, as the temperature decreases, AuHS0, or AuOH0. Mineral associations obtained in model calculations are in general similar to the observed natural types of gold mineralization.

AB - We constructed thermodynamic models of the formation of two types of gold-ore mineralization at the Kagan ultramafic massif in the Southern Urals (Russia). The first type of gold-mineralization is widely spread at the massif in the tectonic zones of schistose serpentinites containing typically ≤ 0.1 ppm Au. The second type of gold-ore mineralization is represented by veined massive, streaky and impregnated magnetite ores in contact with serpentinites. It contains to 5 vol.% sulfides and 0.2–1.2 ppm Au. Our thermodynamic calculations explain the formation of two types of gold-ore mineralization in the bedrocks of ultramafic massifs. Metamorphic water, which is the result of the dehydration of early serpentinites (middle Riphean) during high-temperature regional metamorphism (700 °C, 10 kbar) (late Precambrian), is considered as the source of ore-bearing fluid in the models. The metasomatic interaction of metamorphic fluid with serpentinites is responsible for the gold-poor mineralization of the 1st type at T = 450–250 °C and P = 2.5–0.5 kbar. The hydrothermal gold-rich mineralization of the 2nd type was formed during mixing of metamorphic and meteoric fluids at T = 500–400 °C and P = 2–3 kbar and discharge of mixed fluid in the open space of cracks in serpentinites. The model calculations showed that the dominant forms of gold transport in fluids with pH = 3–5 are AuCl2− complexes (≥450 °C) and, as the temperature decreases, AuHS0, or AuOH0. Mineral associations obtained in model calculations are in general similar to the observed natural types of gold mineralization.

KW - Antigorite serpentinites

KW - Fluid regime

KW - Gold mineralization

KW - Kagan ultramafic massif

KW - Magnetite veins

KW - Native gold

KW - Southern Urals

KW - Thermodynamic modeling

KW - antigorite serpentinites

KW - GOLD

KW - TRANSPORT-PROPERTIES

KW - MINERALS

KW - thermodynamic modeling

KW - SOLID-SOLUTIONS

KW - fluid regime

KW - HIGH-PRESSURES

KW - native gold

KW - O-H

KW - SOLUBILITIES

KW - gold mineralization

KW - ORIGIN

KW - magnetite veins

KW - FLUID

KW - TEMPERATURES

UR - http://www.scopus.com/inward/record.url?scp=85076591728&partnerID=8YFLogxK

U2 - 10.3390/min9120758

DO - 10.3390/min9120758

M3 - Article

AN - SCOPUS:85076591728

VL - 9

JO - Minerals

JF - Minerals

SN - 2075-163X

IS - 12

M1 - 758

ER -