Sr–Nd–Pb isotope systematics of magnetite: Implications for the genesis of Makeng Fe deposit, southern China

The Makeng Fe(− Mo) deposit is the largest Fe deposit in the southwestern Fujian depression belt in southern China. Although it has been extensively studied, there are different views on the genesis of the deposit. In the present study, Sr–Nd–Pb isotope data were used to determine the source of fluids and metals in the deposit. The initial 87Sr/86Sr and εNd (133 Ma) ratios of magnetite samples from Makeng ore vary from 0.71067 to 0.71267 and from − 11.2 to − 8.7, respectively. Ratios for granites vary from 0.70878 to 0.71349 and from − 11.2 to − 8.7, respectively. The magnetite samples yield narrow ranges for 206Pb/204Pb (18.405–18.926), 207Pb/204Pb (15.657–15.710), and 208Pb/204Pb (38.598–38.809). The granites show ranges from 18.787 to 19.154, 15.670 to 15.692 and 39.158 to 39.413 for the same Pb isotopic ratios, respectively. The isotopic data of magnetite and granites shows that the Sr–Nd–Pb isotopic characteristics of magnetite samples are similar to the granites. According to the Sr–Nd–Pb isotopic characteristics, O–H isotopic systematics and rare earth elements characteristics, the initial mineralizing fluids and metals probably originated from granite magmas involving materials from Hercynian diabases or intruded country rocks. Field and laboratory observations suggest that skarn alteration is widespread in the Makeng ore district, indicating that the Makeng Fe deposit is a skarn-type iron deposit.