Age and Origin of the Dongping Au-Te Deposit in the North China Craton Revisited: Evidence from Paragenesis, Geochemistry, and In Situ U-Pb Geochronology of Garnet

Abstract

Dongping is the largest Au-Te vein deposit (~120 t Au) in the North China craton, but its age, origin, and setting remain unsolved. Here, we integrate paragenesis, geochemistry, and in situ U-Pb geochronology of garnet to constrain the timing and possible origin of the Dongping Au-Te deposit. Gold mineralization at Dongping is hosted in the Shuiquangou alkaline complex (ca. 401–390 Ma) and dominated by quartz-sulfide veins with minor ores in adjacent alteration envelopes. Andradite to grossular garnets are recognized in pre-, syn-, and post-ore quartz veins as well as mineralized alteration envelopes and are closely associated with a variety of ore and gangue minerals, mainly including K-feldspar, quartz, specularite, magnetite, pyrite, tellurides, epidote, and calcite. The paragenetic, textural, fluid inclusion, and compositional data suggest that garnets precipitated directly from a low-salinity fluid at 302° to 383°C and 90 to 330 bar. Garnets from various veins and alteration envelopes have similar U contents ranging from 0.80 to 13.89 mg/kg and yield reproducible U-Pb dates of 142 ± 5 to 139 ± 6 Ma (1σ) by laser ablation-inductively coupled plasmamass spectrometry. The dating results suggest that gold mineralization at Dongping occurred in the Early Cretaceous and thus preclude a genetic link between Au-Te mineralization and the ore-hosting alkaline intrusion as commonly suggested. When combined with independent geologic, geochemical, and geochronological studies, the new garnet U-Pb dates allow us to classify the Dongping Au-Te deposit as an oxidized intrusion-related gold deposit, with the causative magma likely derived from melting of an ancient enriched lithospheric mantle source due to destruction of the subcontinental lithospheric keel beneath the North China craton—a catastrophic event induced by the westward subduction of the Paleo-Pacific plate. This study highlights garnet U-Pb dating as a potential robust geochronometer for gold vein deposits elsewhere.

Garnet secondary ion mass spectrometry oxygen isotopes reveal crucial roles of pulsed magmatic fluid and its mixing with meteoric water in lode gold genesis

“…Notably, hydrothermal garnet grains occur in quartz veins of all three paragenetic stages and the mineralized alteration envelopes. The garnet grains yielded U-Pb ages of 142 ± 5 to 139 ± 6 Ma, which are interpreted as the age of gold mineralization at Dongping ( 18 ).…”

“…S1 ), which consists of syenite and minor monzonite. The complex intrudes amphibolite- to granulite-facies rocks of the Neoarchean Sanggan Group (2,715 ± 21 Ma) ( 17 ) and has a zircon U-Pb age of 392 ± 2 Ma ( 18 ). Gold mineralization consists of fault-controlled, high-grade quartz-sulfide veins (3 to 30 g/t Au but locally up to 300 g/t) and low-grade disseminated ores in alteration envelopes (<5 g/t Au).…”

“…Gold mineralization consists of fault-controlled, high-grade quartz-sulfide veins (3 to 30 g/t Au but locally up to 300 g/t) and low-grade disseminated ores in alteration envelopes (<5 g/t Au). On the basis of field relations and petrographic data, three paragenetic stages are well established: 1) a preore stage marked by K-feldspar-quartz-specularite veins; 2) a syn-ore stage largely manifested by quartz-sulfide-magnetite veins and sulfide-magnetite disseminations in alteration envelopes surrounding auriferous quartz veins; and 3) a postore stage represented by barren quartz-calcite veins ( 18 ). Abundant tellurides are present in the syn-ore quartz veins and are sporadically observed in disseminated ores, showing a close association with native gold in both mineralization styles.…”

“…3 ). Based on the garnet formation temperatures determined by fluid inclusion microthermometry in the three paragenetic stages [383 to 302 °C ( 18 )] and the oxygen isotope fractionation equations for andradite-water and grossular-water ( 20 ), δ 18 O water values were calculated to be 5.3 to −4.5‰ for preore vein, 5.5 to −9.1‰ for syn-ore vein, −2.2 to −9.1‰ for postore vein, and 6.1 to 3.1‰ for the mineralized alteration envelope ( Fig. 3 ).…”

“…Dongping garnet formed at the temperature range of 383 to 302 °C ( 18 ), under which oxygen diffusion in garnet can be neglected ( 15 , 16 ). Thus, the measured δ 18 O values represent the original oxygen isotopic compositions of garnet, suggesting that the calculated δ 18 O water values can be reliably used to decipher fluid source and evolution.…”