Mitchell Marcelissen HBSc thesis abstract

Thesis Title: 
Mineral Chemistry of the Gaspé Porphyry, Gaspé, Québec

The Mines Gaspé property hosts multiple Cu-Mo skarn and porphyry orebodies and is located adjacent to the town of Murdochville in the northeastern part of the Gaspé Peninsula, Québec. Both types of orebodies occur within the zoned Copper Brook and overlapping Porphyry Mountain alteration aureoles in calcareous Lower Devonian sedimentary rocks. The strata are intruded by numerous multiphase porphyry sills, dykes, and plugs of Devonian age. Underground and open pit mining at Mines Gaspé ceased in1999 after 141 Mt of 0.9% Cu-equivalent had been extracted from two open pits and eight underground mining areas within the Copper Mountain and Needle deposits. The Porphyry Mountain deposit is the most promising undeveloped resource on the property, containing 437 Mt of ore at 0.89% Cu-equivalent. The Porphyry Mountain intrusion and a sill in the Copper Mountain pit have been dated at 378.80 ± 0.57 Ma and 377.60 ± 0.62 Ma, which better constrains the timing of intrusions at Mines Gaspé than previous studies. Epidote UPb ages at Mines Gaspé overlap within error from 367–352 Ma. Epidote at Mines Gaspé is ~10 million years younger than the Porphyry Mountain intrusion. The time period between the Porphyry Mountain intrusion and epidote formation, as well as the range in epidote ages suggests that the Mines Gaspé system was active for a protracted period of time and more than one generation of epidote is likely, similar to the multiphase occurrence of intrusive units.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses 
of epidote and chlorite from within and between the Copper Mountain and Porphyry Mountain deposits have identified major and trace element spatial variations in mineral chemistry. Epidote analyses show the highest values of Mg, U, Zr, Ti/Co, U/Co, Mg/Sb, and Mg/Zn proximal and As, Mn, Sr, Sr/U, As/U distal to the Porphyry Mountain deposit. Chlorite analyses show the highest values of Li, Ti, V, Ti/Co, Ti/Sb, V/Co, and Zn/Mg proximal and Mn, Zn, Zn/Li, and Zn/V distal to the Porphyry Mountain deposit.

Trace element concentrations in epidote and chlorite show a geochemical footprint surrounding the Porphyry Mountain deposit that allows for the use of mineral chemistry as a tool for vectoring towards porphyry-style mineralisation at Mines Gaspé.