The Triassic Bilugangan deposit: Geological constrains on the genesis of one of the oldest Mo deposits in Inner Mongolia, China

Lili Zhang, Sihong Jiang, Leon Bagas, Yifei Liu

Research output: Contribution to journalArticle

Abstract

The large Bilugangan porphyry Mo deposit is one of the oldest Mo deposit in eastern part of the Central Asian Orogen in Inner Mongolia. The orogen is currently regarded as the most important Phanerozoic region with widespread crustal growth between the Siberian Craton to the north, and North China Block to the south. The Bilugangan Mo mineralisation is hosted by a porphyritic monzogranite and along the contact with the Late Permian Linxi Formation. The mineralisation is disseminated in places and includes various types of hydrothermal veins. The mineralising stages of the deposit includes the pre-ore quartz–K-feldspar(–biotite) pegmatite succeeded by quartz–K-feldspar–molybdenite–muscovite–sericite(–pyrite) veins, quartz–molybdenite–chalcopyrite–perthite–muscovite–sericite(–pyrite–sphalerite), and post-ore quartz–fluorite–calcite (–sericite–muscovite–) veins. Seven molybdenite samples from the mineralisation yield a Re-Os Mo weighted mean date of 238 ± 1 Ma, which is the same, within error, as the Re-Os isochron age of 238 ± 2 Ma, and the ca. 240 Ma age of the porphyritic monzogranite. This is the oldest porphyry Mo – type deposit in the eastern part of the orogen, and the only large –sized Mo deposit in the region, which shows that the east CAO is prospective for Triassic mineralisation. Thirty-three samples of sulfide from the deposit have a narrow δ 34 S VCDT (‰) range of 1.5 to 4.3‰ indicating that the sulfur the sulfur has primarily a magmatic source. The sulfides from the Mo-bearing veins have relatively concentrated Pb isotopic compositions with 206 Pb/ 204 Pb ratios between 18.295 and 19.576, 207 Pb/ 204 Pb ratios between 15.535 and 15.662, and 208 Pb/ 204 Pb ratios between 38.066 and 38.653. These values are consistent with those of the initial Pb isotope ratios for whole rock samples from the porphyritic monzogranite and hornfels. Fifteen gangue quartz samples from various veins define a range of δ 18 O fluid values from 0.5 to 5.2‰ with δD fluid values ranging from −115 to −60‰ indicating that the onset of the mineralising fluid was generated from in-situ degassing of a magmatic source, followed by an input of meteoric water during the late ore-forming stage. It is proposed that the deposit is a collision-related Dabie-type deposit, which is related to the closure of the Paleo-Asian Ocean between the North China Block and Siberian Craton.

Original languageEnglish
Pages (from-to)837-852
Number of pages16
JournalOre Geology Reviews
Volume107
DOIs
Publication statusPublished - 1 Apr 2019

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Triassic
Deposits
mineralization
porphyry
fluid
craton
sulfur
sulfide
Ores
hornfels
molybdenite
gangue
pegmatite
Sulfides
degassing
meteoric water
Phanerozoic
Sulfur
Fluids
feldspar

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@article{24410fdd33d34b4fab6b007687f73a50,
title = "The Triassic Bilugangan deposit: Geological constrains on the genesis of one of the oldest Mo deposits in Inner Mongolia, China",
abstract = "The large Bilugangan porphyry Mo deposit is one of the oldest Mo deposit in eastern part of the Central Asian Orogen in Inner Mongolia. The orogen is currently regarded as the most important Phanerozoic region with widespread crustal growth between the Siberian Craton to the north, and North China Block to the south. The Bilugangan Mo mineralisation is hosted by a porphyritic monzogranite and along the contact with the Late Permian Linxi Formation. The mineralisation is disseminated in places and includes various types of hydrothermal veins. The mineralising stages of the deposit includes the pre-ore quartz–K-feldspar(–biotite) pegmatite succeeded by quartz–K-feldspar–molybdenite–muscovite–sericite(–pyrite) veins, quartz–molybdenite–chalcopyrite–perthite–muscovite–sericite(–pyrite–sphalerite), and post-ore quartz–fluorite–calcite (–sericite–muscovite–) veins. Seven molybdenite samples from the mineralisation yield a Re-Os Mo weighted mean date of 238 ± 1 Ma, which is the same, within error, as the Re-Os isochron age of 238 ± 2 Ma, and the ca. 240 Ma age of the porphyritic monzogranite. This is the oldest porphyry Mo – type deposit in the eastern part of the orogen, and the only large –sized Mo deposit in the region, which shows that the east CAO is prospective for Triassic mineralisation. Thirty-three samples of sulfide from the deposit have a narrow δ 34 S VCDT (‰) range of 1.5 to 4.3‰ indicating that the sulfur the sulfur has primarily a magmatic source. The sulfides from the Mo-bearing veins have relatively concentrated Pb isotopic compositions with 206 Pb/ 204 Pb ratios between 18.295 and 19.576, 207 Pb/ 204 Pb ratios between 15.535 and 15.662, and 208 Pb/ 204 Pb ratios between 38.066 and 38.653. These values are consistent with those of the initial Pb isotope ratios for whole rock samples from the porphyritic monzogranite and hornfels. Fifteen gangue quartz samples from various veins define a range of δ 18 O fluid values from 0.5 to 5.2‰ with δD fluid values ranging from −115 to −60‰ indicating that the onset of the mineralising fluid was generated from in-situ degassing of a magmatic source, followed by an input of meteoric water during the late ore-forming stage. It is proposed that the deposit is a collision-related Dabie-type deposit, which is related to the closure of the Paleo-Asian Ocean between the North China Block and Siberian Craton.",
keywords = "Bilugangan, Eastern Central Asian Orogen, Molybdenite Re-Os age, Porphyry Mo deposit, S-Pb-H-O isotopes",
author = "Lili Zhang and Sihong Jiang and Leon Bagas and Yifei Liu",
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The Triassic Bilugangan deposit : Geological constrains on the genesis of one of the oldest Mo deposits in Inner Mongolia, China. / Zhang, Lili; Jiang, Sihong; Bagas, Leon; Liu, Yifei.

In: Ore Geology Reviews, Vol. 107, 01.04.2019, p. 837-852.

Research output: Contribution to journalArticle

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T2 - Geological constrains on the genesis of one of the oldest Mo deposits in Inner Mongolia, China

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AB - The large Bilugangan porphyry Mo deposit is one of the oldest Mo deposit in eastern part of the Central Asian Orogen in Inner Mongolia. The orogen is currently regarded as the most important Phanerozoic region with widespread crustal growth between the Siberian Craton to the north, and North China Block to the south. The Bilugangan Mo mineralisation is hosted by a porphyritic monzogranite and along the contact with the Late Permian Linxi Formation. The mineralisation is disseminated in places and includes various types of hydrothermal veins. The mineralising stages of the deposit includes the pre-ore quartz–K-feldspar(–biotite) pegmatite succeeded by quartz–K-feldspar–molybdenite–muscovite–sericite(–pyrite) veins, quartz–molybdenite–chalcopyrite–perthite–muscovite–sericite(–pyrite–sphalerite), and post-ore quartz–fluorite–calcite (–sericite–muscovite–) veins. Seven molybdenite samples from the mineralisation yield a Re-Os Mo weighted mean date of 238 ± 1 Ma, which is the same, within error, as the Re-Os isochron age of 238 ± 2 Ma, and the ca. 240 Ma age of the porphyritic monzogranite. This is the oldest porphyry Mo – type deposit in the eastern part of the orogen, and the only large –sized Mo deposit in the region, which shows that the east CAO is prospective for Triassic mineralisation. Thirty-three samples of sulfide from the deposit have a narrow δ 34 S VCDT (‰) range of 1.5 to 4.3‰ indicating that the sulfur the sulfur has primarily a magmatic source. The sulfides from the Mo-bearing veins have relatively concentrated Pb isotopic compositions with 206 Pb/ 204 Pb ratios between 18.295 and 19.576, 207 Pb/ 204 Pb ratios between 15.535 and 15.662, and 208 Pb/ 204 Pb ratios between 38.066 and 38.653. These values are consistent with those of the initial Pb isotope ratios for whole rock samples from the porphyritic monzogranite and hornfels. Fifteen gangue quartz samples from various veins define a range of δ 18 O fluid values from 0.5 to 5.2‰ with δD fluid values ranging from −115 to −60‰ indicating that the onset of the mineralising fluid was generated from in-situ degassing of a magmatic source, followed by an input of meteoric water during the late ore-forming stage. It is proposed that the deposit is a collision-related Dabie-type deposit, which is related to the closure of the Paleo-Asian Ocean between the North China Block and Siberian Craton.

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