辽东青城子矿集区钻孔碳-氧同位素组成及岩脉年代学OA

The Qingchengzi ore concentration area in eastern Liaoning Province is located within the Jiao-Liao-Ji tectonic belt.Since the gold and polymetallic ore deposits are strictly controlled by the"silicon-calcium interface"within transitional zone between the Paleoproterozoic Dashiqiao and Gaixian formations of the Liaohe Group,precise correlations of ore-hosting strata are crucial for regional and deep metallogenic prediction and exploration.This study focuses on 170 marble core samples from the Dashiqiao Formation and 2 granite porphyry core samples intru-ding into the marble,collected from one 1 000 m deep drillhole(ZK12-11)and two 2 000 m deep drillholes(ZK11-8,ZK12-20)recently conducted in the Qingchengzi ore concentration area.Carbon-oxygen isotopic and zir-con U-Pb geochronological analyses were conducted on the marble and granite porphyry samples,respectively.Car-bon-oxygen isotopic results show that the δ13CV-PDB values of the marbles from the three drillholes have no positive anomaly.This suggests that the protoliths of marbles were deposited after the Lomagundi-Jatuli Event(2.33～2.06 Ga or 2.22～2.1 Ga)and stratigraphically correspond to the upper,thin-to medium-bedded,ore-bearing marble member of the Dashiqiao Formation.Therefore,the bottoms of the 1 000～2 000 m drillholes have not yet reached the lower-middle,non-ore-bearing,thick-bedded marble member of the Dashiqiao Formation that are char-acterized by positive carbon isotope anomaly.This finding indicates significant potential for deep metallogenic pre-diction and exploration beneath the currently explored horizons in the Qingchengzi ore concentration area.Zircon U-Pb dating of two granite porphyry samples intruding into the marbles in drillhole ZK11-8 from Taoyuan area yiel-ded crystallization ages of 221±3 Ma and 222±1 Ma,respectively.These results confirm that the emplacement of granite porphyry dykes and the main mineralization epoch in the Qingchengzi area occurred during the Late Triassic at around 220 Ma.In addition,the carbon-oxygen isotopic results demonstrate that the intrusion of dykes and sub-sequent hydrothermal alteration significantly impacted the isotopic compositions of the carbonate rocks,leading to decreases in their δ13CV-PDB and δ18OV-SMOW values.In contrast,regional metamorphism had no significant or inhomo-geneous effect on the carbon-oxygen isotopes of the carbonate rocks.Even within high-grade metamorphosed orogen-ic belts,some marbles may largely retain the primary carbon-oxygen isotopic signatures of their sedimentary proto-liths,and can therefore provide critical evidence for paleoenvironmental studies and regional stratigraphic correla-tion.It is recommended that future deep metallogenic explorations in the Qingchengzi ore concentration area should focus on the upper member of the Dashiqiao Formation near regional faults such as the Jianshanzi and Erdaogou faults showing no positive carbon isotope anomaly,especially the strata with strong hydrothermal alteration and low carbon-oxygen isotopic compositions within this formation,as well as the peripheral zones of Late Triassic granitic porphyry dykes within this sequence.