Hua-Feng Zhang

Significance of zircon trace element geochemistry, the Shihu gold deposit, western Hebei Province, North China

Abstract The Shihu gold deposit is characterized by gold-bearing quartz-polymetallic sulfides and quartz veins. Both Mapeng granitoids batholith and intermediate-basic dikes intruded the metamorphic basement rocks, and are spatially associated with gold mineralization. Trace element abundances in zircons from the Shihu gold deposit, determined by laser-ablation microprobe ICPMS analysis, are sensitive to source rock type and crystallization environment. Concentrations of 21 trace elements were determined for zircons from granitoid rocks, diorites, quartz diorite porphyrites and gold-bearing quartz veins revealed some elemental characteristics and chondrite-normalized trace element patterns from different samples. There were no distinctive differences in REE concentrations of zircons from plutonic rocks and quartz veins, indicating that they probably had the same origin. Relatively flat chondrite-normalized REE patterns with (Yb/Sm)N ratios less than 60 characterized zircons from quartz diorite porphyrites and quartz veins. The highest Nb/Ta ratios were found in zircons from quartz diorite porphyrites, whereas the lowest ratios were found in quartz vein zircons. The Nb/Ta ratios were broadly correlated with HREE+Y contents, and had weak positive correlations with the depth of the Eu negative anomalies. High values U up to 0.4% and Th up to 0.1%, as well as positive correlations with REE+Y characterized zircons from quartz vein. The lowest Th/U ratios of zircons present in quartz veins reflected the relatively high concentration of U in hydrothermal fluid, and high Pb concentrations only typified quartz vein grains relatively enriched in U and Th. Zircons from quartz diorite porphyrites showed the most pronounced Ce anomalies, whereas weak Ce anomalies were typical of zircons from quartz veins, in which Eu/Eu* of zircons had a broadly negative correlation with Ce/Ce*. Trace element geochemistry of zircons from mineralized quartz veins and plutonic rocks confirmed that the sources of ore-forming materials were from Precambrian host rocks. Our results significantly enhanced the usefulness of zircon in crustal studies of the North China craton and as an indicator mineral in mineral exploration of the Taihang region.

Source and evolution of fluids in the Shihu gold deposit, Taihang Mountains, China: evidence from microthermometry, chemical composition and noble gas isotope of fluid inclusions

The well-known Shihu quartz vein-type Au deposit in the Taihang Mountains in the North China Craton (NCC) is hosted by ductile-brittle faults within the Neo-archean–Palaeo-proterozoic Fuping Group metamorphic complex. The deposit exhibit four stages of quartz veins: (1) quartz-K-feldspar-sericite; (2) quartz-pyrite; (3) quartz-polymetallic sulphide; and (4) quartz-carbonate ± pyrite. Three types of fluid inclusions in quartz are recognized in this study. Solid-bearing high-salinity (Type I) fluid inclusions have homogenization temperatures of up to 390 ºC and high salinities of 33–47 wt% NaCl equivalent. Two-phase H2O-rich (Type II) fluid inclusions homogenized between 129–396 ºC and have salinities of 1.7–12.5 wt% NaCl equivalent. Two/three-phase CO2-rich (Type III) fluid inclusions, which are abundant in auriferous quartz veins, have homogenization temperatures of 205–358 ºC and salinities of 1.63–7.64 wt% NaCl equivalent. Laser Raman spectroscopy and quadrupole mass spectrometry confirmed that the vapour phase in the fluid inclusions is dominated by CO2, H2S, CH4, C2H4, N2 and Ar besides H2O, whereas the liquid phase is composed of Cl−, SO42−, Na+, and K+ with minor Mg2+ and Ca2+. Fluid inclusions in pyrite associated with quartz ore-stages (2) and (3) have ΣREE values of 0.61–342.17 ppm with negative Ce, Eu and Y anomalies and LREE enrichment relative to HREE, generally indicating a crustal source of ore fluids. Helium isotope studies of fluid inclusions in pyrites associated with quartz ore-stages (2) and (3) yielded 3He/4He ratios of 0.12–0.93 Ra (Ra=1.4×10−6 for air) and 40Ar/36Ar ratios of 3690–23678. The noble gas data suggest c. 10–20% mantle-derived ore fluids, reflecting an increased interaction of ore fluids with surrounding crustal rocks contributing additional 4He to the fluids. The present data and various information from published works suggest that the Shihu Au deposit was formed during lithospheric thinning or decratonization beneath the Taihang Mountains. The fluids derived from the lower crust, formed due to partial melting and dehydration of the lithospheric mantle, were mixed with magmatic and meteoric waters, and finally precipitated Au and associated metals in the Shihu deposit.

Shared metamorphic histories of various Palaeoproterozoic granulites from Datong–Huai’an area, North China Craton (NCC): constraints from zircon U–Pb ages and petrology

ABSTRACT Different tectonic interpretations have been proposed for the various spatially associated Palaeoproterozoic granulite-facies lithologies (metasedimentary rocks, metabasites, and felsic granulites) from north-central part of the North China Craton, which hinges primarily on controversies about metamorphic histories of these granulites, especially on the timing of peak metamorphism. Published data exhibit two controversial peak metamorphic ages of 1950–1900 Ma and 1850–1800 Ma. We report here LA-ICPMS U–Pb zircon ages of seven representative granulite-facies samples of different lithologies to constrain the timing of metamorphism, and then discuss their geological significance. Most zircon grains from these rocks display weak core-and-rim structures and yield two comparable group metamorphic ages of 1970–1900 Ma and 1880–1790 Ma, although their formation ages vary from Neoarchaean to Palaeoproterozoic. The older population metamorphic ages are interpreted to approximate timing of high-pressure granulite-facies metamorphism, and the younger population ages as the approximate timing of intermediate- to low-pressure granulite-facies metamorphism. Combined with recent petrological studies, we propose these granulites have shared metamorphic histories at least since ~1970–1900 Ma, and they are probably formed in one single metamorphic cycle in response to crustal-scale subduction–collision–exhumation processes involved in Palaeoproterozoic mobile belt. GRAPHICAL ABSTRACT

Thermoluminescence of quartz from Shihu gold deposit, western Hebei province, China: some implications for gold exploration

Thermoluminescence (TL) of monomineralic separates have been widely used in various geosciences fields in order to trace the thermal history and aid in prospecting for gold deposits. Quartz is a ubiquitous mineral in the Shihu gold deposit, which is situated in the northern part of the Taihang orogenic belt in the North China craton (NCC). The deposit is hosted by ductile-brittle faults within an Archean metamorphic core complex of the Fuping Group. This deposit is characterized by gold-bearing quartz-polymetallic sulfides and quartz veins. New TL results have been obtained for quartz, in which four type-TL glow curves were identified. The gold-bearing quartz present type III glow curves that consist of two peak glow curves at the middle and high peak temperatures with the similar TL intensity. In addition, the cross-sections of peak temperatures and TL intensity highlight the valuable area where the Au-bearing quartz present weak TL intensity and low-middle peak temperatures. Our results significantly enhance the usefulness of quartz in metallogenic studies of the North China craton and as an indicator mineral in mineral exploration of the Taihang Mountain region.

Emplacement Depths and Exhumation of Mesozoic Granitoids Responding to Lithospheric Destruction in the Jiaodong Peninsula, North China Craton

The North China Craton (NCC) has experienced lithospheric destruction in Mesozoic accompanied with crustal exhumation. Fission track or (U-Th)/He dating of zircon and apatite for the Mesozoic granitoids in the western Jiaodong Peninsula has been done to reveal history of the crustal uplift (Yang et al., 2016; Sun et al., 2017; Zhang et al., 2017). However, the results solely record the low temperature stage and can reconstruct young thermal history. Widespread plutons exposed at the surface imply apparent exhumation has happened before, nevertheless, the specific timing, amount and rate of exhumation are unknown. Multiple-stage Mesozoic granitoids exposed in the Jiaodong Peninsula provide a compelling case to reveal the crustal exhumation process. In this paper, we use the Al-in-amphibole barometers to estimate emplacement depths of Mesozoic granitoids and to build the exhumation history and mechanism in combination with previous reported mineral Ar-Ar isotopic data.