Study On The Genetic Mechanism And Prospecting Model Of Makeng Iron Deposit In Southwest Fujian

Makeng iron deposit is an important iron polymetallic deposit in southwestern Fujian Province,China.By carrying out geological survey in the mining area,such scientific issues as the genesis types,properties of mineralizing fluids,sources of ore-forming minerals and prospecting criteria of Makeng iron deposit were discussed,and the main metallogenic factors of the deposit were summarized.Based on these above,the prospecting model of“Makeng type”iron deposits was established.In this paper,LA-ICP-MS method was applied to analyze the trace element contents of the magnetite from various iron ores in Makeng iron deposit.The results showed that the content of V,Ti,Cu and Zn was low;furthermore,all analytical data were projected in the skarn area on the?Ca+Al+Mn?-?Ti+V?and?Ti+V?-Ni/?Cr+Mn?discriminate diagrams.Based on these results,it is inferred that Makeng iron deposit is a stratabound skarn iron polymetallic deposit.The similar geochemical characteristics such as mostly light rare earth enrichment and positive europium anomaly of the rare earth elements in the magnetite,garnet,and pyroxene suggested that there is a genetic relationship between these minerals which are formed at high temperature,enriched europium and oxidizing environment.Juzhou and Dayang granites had strong negative europium anomalies,which was complementary to the positive europium anomalies of the magnetite,garnet and pyroxene,indicating that the mineralizing fluids were mainly derived from Juzhou and Dayang granites.The?⁵⁷Fe value of the magnetite in iron ores varied from-0.108‰to 0.344‰,smaller than that of Dayang granite,indicating that Fe was mainly derived from granite.Moreover,the concentration of Fe heavy isotopes of fresh diabase compared to that of altered diabase suggested that part of Fe in altered diabase was in the mineralizing fluids.The?³⁴S value of sulphide minerals varied from-3.2‰to 0.8‰,and the calculated total sulfur isotopic composition(?³⁴S_?S)is of-2.7‰,reflecting magmatic sulfur characteristic,partly mixed with reduced sulfur in surrounding rocks.The trace results showed that lead in the ore was mainly from the upper crust mixed with a small amount of lead in the mantle.In short,the mineralizing materials were mainly derived from Juzhou and Dayang granites,with a small amount derived from the diabase and strata.The analysis results of the altered minerals,elemental concentrations and magnetic susceptibilities by scanning the cores from ZK614 and ZK617 boreholes showed that Markeng iron deposit was typically characterized by its skarn-type alternated mineral distribution.The distribution range of As and Sn was almost the same as that of magnetite mineralization.Furthermore,the content of As and Sn showed a certain positive correlation with that of Fe.Mineral alteration zones,Silicon calcium surface,pyroxenite,as well as As and Sn geochemical anomalies were the important mineral prospecting criteria of Makeng iron deposit.The above research results indicated that the main metallogenic factors of“Makeng type”iron deposits could be summarized as follows:the main metallogenic geological bodies are the late Mesozoic granites intruded in about130Ma,while the secondary metallogenic geological bodies are the Palaeozoic and Mesozoic diabases;ore-controlling tectonics mainly include nappe tectonics,detachment structures and folds;metallogenic structure surfaces are mainly of silicon-calcium surfaces between Lindi formation?C₁l?and Jingshe-Qixia formations?C₂j-P₂q?,and between Wenbishan formation?P₂w?and Jingshe-Qixia formations;and the mineralization are characterized by the zonal distribution of the altered minerals,the widely developed silicification belts in Lindi formation?C₁l?,and magnetite mineralization,molybdenum mineralization and lead-zinc mineralization,etc.