In situ LA-ICP-MS Determination of Trace Elements in Magnetite from a Gypsum-Salt Bearing Iron Deposit and Geochemical Characteristics

Gypsum-salt formation affects the oxygen fugacity of ore-forming fluid and changes the fluid composition, and then affects the trace element composition, which plays an important indicator role in the formation of iron ore deposits. Therefore, changes in the elemental composition of magnetite can be used to classify the types of deposits and determine their genesis. Gypsum-salt formation is widely developed in "Pamir-type" iron deposits in Xinjiang and Ningwu iron deposits in the middle and lower part of the Yangtze River. However, the controlling mechanism of gypsum-salt formation is still unclear.

In order to investigate the metallogenic process and formation environment of the two types of magnetite, and to discuss the role of gypsum-salt formation in the formation of magnetite deposits.

In situ LA-ICP-MS were employed to determine trace elements in magnetite. RESULTS: LA-ICP-MS results showed that magnetite in the Ningwu area were mainly rich in Ti and V, indicating that it was closely related to magmatism, while the contents of Nb, Ta, Zr, Hf and other high field strength elements (HFSE) in magnetite in the Tashkurgan magnetite deposit in Xinjiang were depleted. Combined with the discrimination diagram of magnetite types, it was mainly divided into two genetic types: magmatic hydrothermal magnetite and hydrothermal metasomatic skarn magnetite related to marine volcanic activity.

The results show that the gypsum-salt formation changes the oxygen fugacity during the formation of magnetite deposits in the Tashkurgan area, and provides an important source of ore-forming material for mineralization during the formation of porphyrite-type iron ore in the Ningwu area.