Accessory Minerals in New Idria serpentinite

SMSU Event Center BC

Serpentinite is a rock composed almost wholly of serpentine-group minerals and contain accessory minerals that are sensitive to formation chemical condition. In 2017 Patton did a study on accessory minerals of an ophiolite. The New Idria serpentinite is a forearc serpentinite diapir that rose from great depth in a subduction zone where the formation conditions are not like an ophiolite, they experienced subducted high-pressure. This study looks at New Idria accessory minerals to see how subduction effects their formation and to see if their accessory minerals are different and how are they affected by subduction. Thorough analysis of five samples of New Idria peridotite using x-ray diffraction, optical microscopy, reflected-light microscopy, energy-dispersive x-ray spectroscopy from a scanning electron microscope determined the formation conditions of the fluid that formed the New Idria peridotite. These analyses found two types of mineral assemblages; sulfide free and sulfide bearing. All samples showed in order of abundance: chromite, magnetite and awaruite. In the less common sulfide bearing rocks the accessory minerals also contained sulfide minerals of much smaller abundance and size: heazlewoodite, linnaeite, and pentlandite. There is a distinctive lack of sulfide minerals compared to the ophiolite peridotite, which suggests low sulfur in the low grade forearc.