Origin of the Shangfang Tungsten Deposit in the Fujian Province of Southeast China: Evidence from Scheelite Sm–Nd Geochronology, H–O Isotopes and Fluid Inclusions Studies

Abstract

The Shangfang deposit is a recently discovered large-scale tungsten deposit (66,500 t at 0.23% WO3), which is located near the western boundary of the Southeastern Coastal Metallogenic Belt (i.e., Zhenghe–Dafu fault), and adjacent to the northeast of the Nanling Range Metallogenic Belt. Unlike many other W–Sn deposits in this region that occur within or near the granites, the orebodies in the Sangfang deposit all occur within the amphibolite of Palaeoproterozoic Dajinshan Formation and have no direct contact to the granite. In this study, we carry out a thermal ionization mass spectrometer (TIMS) Sm-Nd isotope analysis for the scheelites from the orebody, which yields a Sm–Nd isochron age of 157.9 ± 6.7 Ma (MSWD = 0.96). This age is in good agreement with the previously published zircon U–Pb age (158.8 ± 1.6 Ma) for the granite and the molybdenite Re–Os age (158.1 ± 5.4 Ma) in the deposit. Previous studies demonstrated that the W–Sn deposits occurring between Southeastern Nanling Range and Coastal Metallogenic Belt mainly formed in the two periods of 160–150 Ma and 140–135 Ma, respectively. The microthermometry results of fluid inclusions in scheelite and quartz are suggestive of a near-isothermal (possibly poly-baric) mixing between two fluids of differing salinities. The H–O isotope results illustrate that the ore-forming fluids are derived from magma and might be equilibrated with metamorphic rocks at high temperature. The Jurassic granite pluton should play a critical role for the large hydrothermal system producing the Shangfang W deposit. Furthermore, the negative εNd(t) of −14.6 obtained in the Shanfang scheelite suggests for the involvement of the deep crustal materials. In general, subduction of the paleo-Pacific plate caused an extensional tectonic setting with formation of the Shangfang granites and related W mineralization, the geological background of which is similar to other W deposits in the Nanling Range Metallogenic Belt.

Geochemistry and Origin of Scheelites from the Xiaoyao Tungsten Skarn Deposit in the Jiangnan Tungsten Belt, SE China

“…Scheelite (CaWO 4 ) is one of the dominant tungsten-containing minerals in porphyry-skarn W deposits, quartz vein W and Au-W deposits, and some metamorphic Au deposits [1,2]. Scheelite incorporates relatively high amounts of REE and Sr in substitution for Ca [3,4], and has been used to characterize the ore-forming fluids [5][6][7][8] and the genetic type of deposits [9][10][11]. The REE patterns in scheelite are highly sensitive to the hydrothermal evolution, making scheelite act as a promising tool to understand prevailing hydrothermal conditions [3,4].…”

Editorial for the Special Issue “Development of W-Sn and Rare-Metal Metallogenic Systems in an Orogenic Belt”

“…Zhu et al [5] describe a recently discovered atypical and very large tungsten deposit (66,500 t at 0.23% WO 3 ), the Shangfang deposit, occurring within Paleoproterozoic amphibolites, away from any contact with granitic bodies, contrarily to what is commonly observed in other occurrences. This study is also remarkable by the very good reproducibility in the age determinations obtained by a variety of isotopic systems; thermal ionization mass-spectrometer Sm-Nd isotope analysis of scheelite from the orebody yielded similar ages as previously published U-Pb ages on zircon from nearby granites and Re-Os ages of molybdenite from the mineralization.…”