Tungsten-bearing rutile from the Jiaodong gold province, Shandong, China and its implication for gold mineralization

Electron-microprobe analysis and X-ray micro-diffraction show the presence of tungsten-bearing rutile in the Jinling, Jiaojia, Linglong and Hexi gold deposits in the Jiaodong gold province. The tungsten-bearing rutile appears both in gold-bearing quartz veins and alteration fracture zones as columnar, tabular and irregular crystals with grain sizes ranging from 2 to 300 μm in association with sericite, quartz, hematite and electrum. The contents of W, coupled with Fe, Nb and V, are heterogeneously distributed in rutile with maximum contents of W 8.61 wt%, Fe 3.35 wt%, V 3.08 wt%, Nb 5.56 wt%. Tungsten content shows a prominent positive correlation with Fe and V and the coupled substitutions of W, Fe, V and Nb for Ti abide mainly by 2(Fe, V)³⁺ + W⁶⁺ = 3Ti⁴⁺ and Fe³⁺ + Nb⁵⁺ = 2Ti⁴⁺, indicating that Fe and V are mainly trivalent, and Nb mainly pentavalent. X-ray micro-diffraction and Raman spectra show that the tungsten-bearing phase has the tetragonal rutile structure in space group P4₂/mnm with the unit-cell parameters a = 4.595(1) Å, c = 2.9609(2) Å for a crystal with 3.20 wt% W on average. The textural relationship of tungsten-bearing rutile in the ores indicates that it was formed in the hydrothermal stage in a relatively oxidizing and alkaline environment.