Geochemistry, Geochronology, and Fluid Inclusion Study of the Newton Epithermal Gold, and Morrison Porphyry Copper Deposits, British Columbia

• Author / Creator

  Liu, Lijuan

• Petrologic, geochemical, geochronological, and fluid inclusion studies were conducted on the Newton epithermal and Morrison porphyry deposits in central British Columbia, as a part of a large collaborative research project to combine geological, ZTEM, magnetotelluric, and magnetic studies, in order to improve the effectiveness of ZTEM surveys for deep mineral exploration. Newton is an intermediate-sulfidation epithermal gold deposit, which is spatially and genetically related to a Late Cretaceous volcanoplutonic complex. The mineralized felsic volcanic rocks, feldspar-quartz-hornblende porphyry, and quartz-feldspar porphyry from the volcanoplutonic complex yielded U-Pb zircon ages of 72.1 ± 0.6 Ma (Amarc Resources Ltd., unpublished data, reported in McClenaghan, 2013), 72.1 ± 0.48 Ma (new data), and 70.9 ± 0.5 Ma (Amarc Resources Ltd., unpublished data, reported in McClenaghan, 2013), respectively. A barren diorite intrusion yielded a slightly younger U-Pb age of 69.32 ± 0.43 Ma. Gold occurs as electrum and gold-silver telluride, which are present as inclusions in disseminated pyrite and marcasite. Three stages of mineralization are recognized: (1) disseminated pyrite with gold inclusions, and rare quartz-pyrite ± molybdenite veins; (2) disseminated marcasite with gold inclusions; (3) polymetallic pyrite-chalcopyrite-sphalerite-arsenopyrite veins. Molybdenite from a porphyry-hosted stage 1 quartz-calcite-pyrite-molybdenite vein yielded a Re-Os data of 72.1 ± 0.3 Ma (McClenaghan, 2013), which is taken to represent the age of mineralization. A relatively hot and saline hydrothermal fluid was related to stage 1 mineralization, and homogenization temperatures and salinities of fluid inclusions in a stage 1 quartz–pyrite ± molybdenite ± gold vein average 313 ± 51°C (n = 82) and 4.8 ± 0.9 wt.% NaCl equiv. (n = 46), respectively. The predominance of disseminated mineralization suggests that wallrock reaction and cooling were the main controls on gold precipitation, although evidence for boiling was also observed in the veins. Morrison is a typical porphyry Cu-Au-Mo deposit, spatially and genetically related to Eocene plagioclase-hornblende-biotite porphyry intrusions. The porphyry intrusions are part of a calc-alkaline to high-K calc-alkaline diorite to granodiorite intrusive suite with continental arc affinity, and yielded a U-Pb age of 52.21 ± 0.37 Ma. The mineralization can be divided into 3 stages: (1) disseminated and vein-type chalcopyrite-bornite; (2) quartz-molybdenite-pyrite veins; and (3) polymetallic dolomite ± quartz-sphalerite-galena-arsenopyrite-chalcopyrite veins. Molybdenite yielded ages of 52.54 ± 0.22 and 53.06 ± 0.22 Ma, which are broadly consistent with the age of the porphyry intrusions, indicating a genetic relationship. Fluid inclusion (Th = 400 to 526°C; salinity = 39.8 to 47.8 wt.% NaCl equiv.), sulfur isotope (δ34S = -0.2 and 0.8‰ for pyrite and chalcopyrite intergrowths), and oxygen isotope (δ18Ofluid = 3.7 to 6.3‰) data for stage 1 mineralization indicate that the early Cu-Au-bearing fluids were likely of magmatic origin. A cooler and slightly less saline fluid (Th = 320 to 421°C; salinity = 37.0 to 43.1 wt.% NaCl equiv.) was responsible for stage 2 mineralization. Sulfur isotope (δ34S = -2.1 and -1.2‰ for molybdenite and pyrite, respectively) and oxygen isotope (δ18Ofluid = 0.3 to 3.4‰) data from stage 2 minerals suggest a contribution from meteoric groundwater and sediment-derived S to fluids still dominantly of magmatic origin. Stage 3 was associated with cooler and much more dilute fluids (Th = 163° to 218°C; salinity = 3.1 to 3.9 wt.% NaCl equiv.), with oxygen isotopic compositions of δ18Ofluid ≈ -2 to +4‰ from early vein quartz, and 0.8 to 6.3‰ from late vein dolomite, sulfur isotopic compositions for sphalerite and pyrite of δ34S = -7.1 and -5.6‰ (respectively), and carbon isotopic compositions from dolomite of δ13C = 0.6 and 0.7‰. These characteristics suggest that stage 3 fluids were likely dominantly of meteoric water origin (with some wallrock isotopic exchange), and derived C and S from the sedimentary country rocks. The results of this study will be used to constrain geological and petrophysical models that are being developed to improve the effectiveness of ZTEM surveys.

• Subjects / Keywords

  • Geochemistry
  • Newton epithermal
  • Fluid inclusion
  • Morrison porphyry
  • Geochronology

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3QJ78611

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.