In situ geochemical data were obtained for pyrite crystals and native gold from two distinct vein sets in the Grass Valley gold district, California. Samples of the N-S (north-south-trending) veins were collected underground at the Empire Mine State Historic Park and samples of the E-W (east-west-trending) veins were collected from drill core provided by the Idaho-Maryland Mining Corporation in 2008. These geochemical data were analyzed to better understand paragenesis of quartz veins in orogenic gold deposits. Data includes electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) chemistry and LA-ICP-MS sulfur isotope values for pyrite crystals, and EPMA geochemistry of native gold grains found within the orogenic gold veins. The geochemical results presented in this data release were analyzed at the U.S. Geological Survey in Denver, Colorado.
Electron probe microanalyses were performed using a JEOL 8900 electron microprobe with five wavelength dispersive X-ray spectrometers. Operating conditions included a beam current of 100 nano-ampere (nA) measured on the Faraday cup, a focused electron beam, and an accelerating voltage of 20 kiloelectron-volt(keV).
Minor and trace element geochemistry was determined by LA-ICP-MS using a Photon Machines Analyte (193-nanometer (nm) excimer) coupled to a PerkinElmer DRC-e ICP-MS using a spot size of 25 micrometers (µm).
In situ sulfur isotope data was collected using a Nu Instruments high-resolution MC-ICP-MS via a 193-nm wavelength GS excimer laser ablation system with spot sizes varying from approximately 25-55 µm.