Geological And Geochemical Characteristics Of Hongqiling Cu-Ni Sulfide Deposit And Prospecting Techniques For The Same Type Deposit

Hongqiling deposit is a magmatic Cu-Ni sulfide deposit that ranks second in China. Thegeological characteristics of Cu-Ni deposit, temporal and spatial distribution of mafic-ultramafic intrusions and the geological and geochemical characteristics of metallogenicintrusions have been studied systematically in this thesis, to deepen the understanding of itsmetallogenic mechanism. The effectiveness of various prospecting methods is studied and theprospecting technical process for this type Cu-Ni sulfide deposits has been carried out for thefirst time.Hongqiling Cu-Ni deposit is located in the east of Xing’an-Mongolia Orogenic belt, theintersection of Xing’an geosyncline and Sino Korean paraplatform. The stratum outcroppedare mainly the Cambrian-Ordovician Hulan Group metamorphic rocks of Lower Paleozoic inHongqiling mine field and Shoushangou formation clastic rock series of Lower Permian inChajian mine field. NW-trending faults induced by the NE-trending Huifahe deep fracture arethe rock and ore controlling structures. Meanwhile, they are also the ore leading and hostingstructures of the deposit.Hongqiling Cu-Ni deposit includes two mine fields, Hongqiling and Chajian. There arethree mafic-ultramafic zones in Hongqiling mine field. Metallogenic intrusions such as No.1,No.7, No.3, No.2and No.32as well as other non ore-bearing intrusions such as No.33andNo.23are located in zone Ⅰ, most of which are multi-lithofacies. The lithofacies of zoneⅡand Ⅲ are relatively simple with no industrial ore-body. Intrusions in zoneⅡcharacterizedby gneissic structures generally. Chajian mine field also comprise three mafic-ultramaficzones. There are No.8and No.9intrusion distributed in western ultramafic sub zone, No.1,No.2, No.14, No.10and No.5intrusion in Houshui-Chajian-Nanshui mafic-ultramafic subzone and No.3, No.6, No.7intrusion in Heping-Qijia-Shangfutai mafic-ultramafic sub zone.Among them, No.1, No.9and new No.6intrusion are metallogenic intrusions. Themetallogenic intrusions in Hongqiling Cu-Ni deposit all formed in Indosinian. The ages ofmetallogenic intrusions in Chajian mine field is slightly older, shows a trend that therock-forming ages of metallogenic intrusions become younger from southwest to northeastgradually. There are mainly three types of lithofacies association of the metallogenic intrusions:type No.1, No.7and No.3. The lithofacies association of type No.1is gabbro+pyroxenolite+pyroxene+peridotite+olivine-websterite, and ore-bearing lithofacies are lherzolites. Type No.7intrusion includes websterite+pyroxene peridotite, and they are also the ore-bearinglithofacies. No.3intrusion includes gabbro+anorthose-bearing hornblende pyroxenite+olivine-websterite, and the ore-bearing lithofacies are mainly anorthose-bearing hornblendepyroxenites. The olivines and orthopyroxenes are magnesium-rich in all intrusions ofHongqiling mine field. The olivines belong to chrysolite and En of orthopyroxenes isgenerally above80%. Clinopyroxenes in metallogenic intrusions mainly belong to diopside,augite and pigeonite-augite with great variation in chemical composition, especially thevariation of clinopyroxene Di end member. Amphiboles in metallogenic intrusions all belongto calcic amphibole with great variation in chemical composition.The chemical composition of metallogenic intrusions varies greatly. It shows that thecharacteristic of strong magma differentiation. The ratio (m/f) of No.1intrusion ranges from2.69to5.99with an average of4.79, and Mg~#ranges from73.40to85.89with an average of82.31. No.7intrusion ranges from1.01to5.03with an average of3.75, and Mg~#ranges from50.49to83.84with an average of77.44. The ratio (m/f) of No.3intrusion ranges from0.74to5.11with an average of2.98, and Mg~#ranges from42.76to83.84with an average of72.58.The metallogenic intrusions all belong to iron ultrabasic rocks by constituents.The enrichment of U, K and Pb and relative loss of Nb, Ta in metallogenic intrusions aretheir intrinsic geochemical characteristics which have no relationship with magma evolutionand differentiation. Stable isotope Nd indicates that the metallogenic magma originated fromdepleted mantle. The research on Sr, Os shows that metallogenic intrusions all have obviouscrustal contamination, and the found of capture zircon in metallogenic intrusions provides adirect evidence for crustal contamination. Comprehensive study shows that the magmaoriginated from depleted mantle and was affected by crustal contamination.Rare earth elements and PGE characteristics show that metallogenic intrusionsunderwent obvious magmatic fractional crystallization. The mineralization of No.1and No.3intrusions are mainly in-situ liquiation, while No.7intrusion is liquation at deep-level. Strongfractional crystallization and crustal contamination are the main mechanism promoting thesulfur supersaturated and sulfide liquated to mineralize. Superimposition-reformation of thelatter metallogenic stage hydrotherm acts a part in the re-enrichment for mineralization, evenPGE-rich hydrothermal vein-like ore bodies exist (especially in deep No.7intrusion). Theappearance of alteration, diorite pegmatite and products of hydrothermal such as sulfide-quartz are the significant geological signs of metallogenic intrusions. According to the geological thermobarometer of rock-forming minerals, the calculatedtemperature of crystallization beginning of olivines in metallogenic intrusions is1400℃-1500℃. Eutectic temperature of websterite is1000℃-1200℃. Condensation and console-dation temperature of metallogenic intrusions is slightly lower than that of none-metallogenicintrusions, which is related to high volatile components in metallogenic intrusions. Thediagenetic pressure and depth of the metallogenic intrusions are3.7to6.2kb and12.3to20.7km. The metallogenic temperature is300℃-500℃. The metallogenic depth is consistentwith diagenetic.The research shows that the mafic-ultramafic rocks related to magmatic sulfide depositsare located in the plate margin, boundary between platform and geosyncline or secondaryfaults of the deep fracture in the orogenic belt. The better mineralized mafic-ultramaficintrusions often have a prominent Ni abnormalities and high Ni/Co in1:200000streamsediment. The indication effect of Ni, Ni/Co is not obvious when the level of mineralization islow or the scale of mafic-ultramafic intrusion is small. In medium-scale aeromagneticprospecting, mafic-ultramafic intrusions are often located in banded, lined and beadednegative magnetic anomaly zones or the boundary between positive and negative anomalies.Mafic-ultramafic intrusions have good correlations with large-scale high magneticanomalies, the high value gravity traps and Ni, Co, Cu combination anomalies. Thehigh-precision geomagnetism, gravity and geochemical soil survey are effective ways formafic-ultramafic intrusions prospecting. Geological and geochemical evaluation of theintrusions is the best way to screen metallogenic intrusions and find ore bodies. Transientelectromagnetic method is an effective mean for positioning the Cu-Ni sulfide ore bodies,controlled source audio-frequency magnetotellurics and geo-electrochemical method alsopossess certain effects.Prospecting technology process for magmatic Cu-Ni sulfide deposits can be grouped intofour stages: strategic area selection stage, intrusions positioning stage, intrusions evaluationstage and ore bodies positioning stage. Strategic area selection stage: distribution prospect ofmafic-ultramafic intrusions are determined by tectonic setting, regional geochemicalexploration and aeromagnetic anomalies. Intrusions positioning stage: mafic-ultramaficintrusions are determined by high-precision geomagnetic and gravity measurement and soilgeochemical measurement. Intrusions evaluation stage: ore-bearing potential of mafic-ultramafic intrusions are evaluated by geological and geochemical characteristics. Ore bodiespositioning stage: deep ore bodies are located by means of transient electromagnetic method,controlled source audio-frequency magneto-tellurics and and geo-electrochemical method.