Mineralogy Of Borate Minerals In The Yeshan Skarn-type Boron Deposit, Jiangsu

The Yeshan skarn, Jiangsu, contains one of the most important boron deposits in China. By using scanning electron microscope, electron probe micro-analyzer, powder X-ray diffraction, and Laser Raman spectrometer, we studied the petrographic and mineralogical features of szaibelyite and ludwigite from this skarn-type boron deposit. Four types of szaibelyite have been distinguished in this boron deposit:Ⅰ) Massive szaibelyite, which usually encloses serpentine and brucite;2) Fibrous szaibelyite, which forms intergrowths with fine-grained magnetite and encloses ludwigite;3) Net-like szaibelyite, which cross-cut early massive szaibelyite; and4) Interstitial szaibelyite, which fills the interstitial space of other phases. We propose that massive szaibelyite could have formed by the interaction between B-rich hydrothermal fluid and brucite. The fibrous szaibelyite could have formed by the interaction between B-rich fluid and ludwigite. The net-like and interstitial szaibelyite could have directly precipitated from late-stage B-rich fluids.There are at least two types of ludwigites in the deposit. The first type of ludwigite is associated with serpentine and coarse-grained magnetite. The second type of ludwigite which are surrounded by fibrous szaibelyite and fine-grained magnetite is associated with hematite. The two types of ludwigite have different Al2O3and MgO contents. The difference in mineral composition may reflect the various compositons of hydrothermal fluids, especially in the concentrations of Mg and Al. The different mineral assemblages of ludwigite may indicate the different of redox environment after the formation of ludwigite.