OCCURRENCE AND REMOBILIZATION OF GOLD IN THE DAYINGEZHUANG DEPOSIT IN JIAODONG, NORTH CHINA CRATON: EVIDENCE FROM TEXTURAL AND GEOCHEMICAL FEATURES OF PYRITE

Abstract

THE DAYINGEZHUANG GOLD DEPOSIT IN THE JIAODONG DISTRICT, EASTERN MARGIN OF THE NORTH CHINA CRATON IS HOSTED IN MESOZOIC GRANITIC ROCKS AND CONSISTS OF QUARTZ-SULFIDE VEINS/VEINLETS AND SULFIDE DISSEMINATIONS IN ALTERATION ENVELOPES. PREVIOUS STUDIES MAINLY FOCUSED ON THE GEOCHRONOLOGY, SOURCES OF ORE-FORMING FLUIDS AND METALS TO INVESTIGATE THE ORE GENESIS. HOWEVER, ENRICHMENT MECHANISM OF AU AND OTHER ASSOCIATED TRACE METALS REMAIN UNCLEAR. IN THIS STUDY, WE PRESENT DETAILED TEXTURES AND IN-SITU LA-ICP-MS TRACE-ELEMENT COMPOSITIONS OF DIFFERENT GENERATIONS OF PYRITE, AS WELL AS EMP ANALYSIS OF AU-BEARING MINERALS TO DISCUSS THE OCCURRENCE AND ENRICHMENT MECHANISM OF AU AT THIS DEPOSIT. THREE GENERATIONS OF PYRITE (PY1, PY2 AND PY3) FORMED DURING THREE HYDROTHERMAL ORE STAGES (I, II, AND III) AT DAYINGEZHUANG. PY1 OCCURS AS DISSEMINATIONS IN SERICITIC ALTERATION ASSEMBLAGES AND IS CHARACTERIZED BY LOW AU (MEAN 0.15 PPM), AG, AS AND TE CONTENTS. THE TIME-RESOLVED DEPTH-CONCENTRATION PROFILES INDICATE THAT AU IN PY1 MAINLY OCCURS AS NANOPARTICLES AND/OR MICRON-SIZED INCLUSIONS. PY2 CAN BE FURTHER DIVIDED INTO THE EARLY UNDEFORMED PY2A AND LATER PY2B, WHICH IS THE PRODUCT OF DEFORMED PY2A WITH DIFFERENT DEGREES OF BRITTLE TO PLASTIC DEFORMATION AND RECRYSTALLIZATION. PY2A IN PYRITE-SIDERITE-QUARTZ VEINS IS RELATIVELY ENRICHED IN INVISIBLE AU (MEAN 0.41 PPM), AG, AS, AND TE COMPARED TO PY1, AND CONTAINS NUMEROUS MICRON-SIZED AU INCLUSIONS. IN CONTRAST, PY2B CONTAINS LESSER INVISIBLE AU (0.21 PPM) AND HOST ABUNDANT GOLD MINERALS ALONG THE GRAIN BOUNDARIES AND MICROFRACTURES. PY3 IN POLYMETALLIC SULFIDE VEINS HAS LITTLE AU. AS A WHOLE, AU IN PYRITE IS POSITIVELY CORRELATED WITH AG AND TE, WHICH IS CONSISTENT WITH THE RESULTS OF EMP ANALYSIS SHOWING THE OCCURRENCE OF AU AS ELECTRUM, NATIVE GOLD AND MINOR PETZITE IN PYRITE. SUCH EVIDENCES SHOW THAT THE DEFORMATION AND RECRYSTALLIZATION OF AURIFEROUS PY2A POTENTIALLY CAUSED LOCAL REMOBILIZATION OF AU (MAINLY AS MICRON-SIZED INCLUSION AU) VIA SOLID-STATE DUCTILE FLOW AND SUBSEQUENT RECONCENTRATION OF AU IN MICROFRACTURES OF PY2B. THE PYRITE DEFORMATION AND AU REMOBILIZATION EVENTS WERE SUGGESTED TO BE RELATED TO THE CONTINUOUS REACTIVATION OF THE REGIONAL ZHAOPING FAULT CONTEMPORANEOUS WITH GOLD MINERALIZATION. OUR STUDY HIGHLIGHTS THE IMPORTANCE OF REMOBILIZATION AND RECONCENTRATION OF AU TRIGGERED BY SYN-ORE TECTONIC ACTIVITIES AT DAYINGEZHUANG AND POSSIBLY OTHER AU DEPOSITS IN THE JIAODONG DISTRICT.