The nature and significance of lithogeochemical and stable isotope alteration halos in the Hollinger-McIntyre gold deposit, Ontario, Canada

Two distinct mineralizing fluids formed the Hollinger-McIntyre-Coniaurum (HMC) deposit. The earliest fluid is associated with emplacement of a disseminated Cu-Au-Mo zone in the Pearl Lake Porphyry (PLP). The alteration pattern of the felsic rocks in the PLP is characterized by increased concentrations of K2O, Au, Cu, Mo, W, and Sn, and K/Al, Sericite / Chlorite (SCI) and Sericite Alteration Indexes and the removal of CaO, relative to nearby “unaltered” rocks. The H2O-CO2-NaCl mineralizing fluid that altered the PLP had a temperature between ~340° and 390°C, and a δ18Owater composition of 11.68 to 12.68 ‰. The H2O-CH4-CO2-NaCl mineralizing fluid that deposited gold in and above the Hollinger Shear Zone (HSZ) had an estimated temperature of 290°C and a δ18Owater of 4.60 ‰. This gold-bearing fluid is associated with increased concentrations of As, CO2, and CO2/CaO and removal of Na2O from rocks in and above the HSZ. The isotopic composition of the auriferous fluid is similar to those that formed the Giant and Colomac deposits. Formation of the HMC Cu-Au-Mo and Au deposits by two geothermal systems with chemically distinct fluids has important implications for geochemical exploration efforts in the Porcupine Mining Camp and elsewhere. KEYWORDS: Hollinger, McIntyre, gold, mesothermal, lithogeochemical, alteration, stable isotopes