Characterization of Alkalic & Calcalkalic Porphyry Clusters: Woodjam District, central British Columbia
(093A)

- F. Bouzari, C. Hart and I. del Real; MDRU

Woodjam Porphyry Clusters Study Late Triassic to Middle Jurassic porphyry deposits in British Columbia are characterized as end members having calc‐alkalic or alkalic affinities (Barr et al., 1976; McMillan et al., 1995; Lang et al., 1995) with both categories, locally occurring as clusters such as at the Highland Valley calc‐alkalic and Mt. Polley alkalic camps. Recent exploration success in the Woodjam camp shows that a cluster of multiple porphyry centres with a narrow age (ca. 197 Ma: MDRU, unpublished) at the margin of the Takomkane batholith have alkalic (e.g., Megabuck), calc‐alkalic (e.g., Southeast Zone), and alkalic to calc‐alkalic characteristics (Deerhorn). Thus, indicating that mineralization in the Deerhorn system seems to have evolved from alkalic to calc‐alkalic host‐rocks and alteration assemblages. Woodjam therefore provides an opportunity to better understand the relationships between alkalic to calkalkalic magmatism and related mineralization, a feature that remains poorly understood.

The Woodjam camp provides an excellent locality to develop and increased understanding the significance of these varying geological characteristics. Such knowledge can significantly aid exploration decisionmaking, especially around known porphyry camps, and will provide critical links between these two, apparently end‐member systems. Therefore, this research project is being undertaken in collaboration with Geoscience BC and Gold Fields Canada Exploration, to better characterize the Woodjam porphyry cluster in central British Columbia.

The main objectives of the project are to characterize the host‐rocks and nature of mineralization and alteration at several selected porphyry centers, and to determine their relationships of alkaline and calcalkalic characteristics. These will be integrated with the magmatic evolution in order to establish a model of the evolution of porphyry clusters at Woodjam, and indicate controlling features of alkaline and calc‐alkaline ore types. This will be accomplished through field investigations and various laboratory techniques.

Posters and Presentations
2013: Southeast Zone (Cu-Mo) and Deerhorn (Cu-Au) Porphyry Deposits: Paragenesis, Alteration and their Possible Relationships, Woodjam Property, Central British Columbia
- Mineral Exploration Roundup Poster (pdf, 11 MB)
Technical Articles
2013: "Paragenesis and alteration of the Southeast Zone and Deerhorn porphyry deposits, Woodjam property, central British Columbia"
- Summary of Activities 2012, Report 2013-1 p. 79-90 (pdf, 6.8 MB)

2014: "Relationships between calcalkalic and alkali mineralization styles at the copper-molybdenum Southeast Zone and copper-gold Deerhorn porphyry deposits, Woodjam property, central British Columbia"
- Summary of Activities 2013, Report 2014-1 p. 63-82 (pdf, 17.9 MB)
Final Deliverables
M.Sc. Thesis - I. Del Real
Geology, alteration, mineralization and magmatic evolution of the Southeast Zone (Cu-Mo) and Deerhorn (Cu-Au) porphyry deposits, Woodjam, central British Columbia, Canada - University of British Columbia, 2015 - Available digitally through UBC (pdf, 36.5MB)

Abstract: The Woodjam district is part of the porphyry deposits of Late Triassic to Middle Jurassic age (216--183 Ma) located in the Quesnel terrane in central British Columbia. Porphyry centers include the large Cu-Mo Southeast Zone (SEZ), hosted in the calc-alkalic Takomkane batholith, and the Au-Cu Deerhorn, Megabuck and Takom deposits. The latter are peripheral to the margin of the batholith and are associated with smaller monzonitic bodies of more mafic affinity that intrude and mineralize Nicola Group strata. The Takomkane batholith, host to the SEZ, intrudes and underplates the Nicola Group strata. The main phases include coarse-quartz-monzonite (CQM; 197.480.44 Ma) and a later, fine-grained-quartz-monzonite (FQM). Alteration is zoned from intense K-silicate in the center, weaker towards the margins, surrounded by albite alteration at the margins. Mineralization is zoned from chalcopyrite to pyrite-dominated at the margins. The Deerhorn deposit is centered on narrow monzonite bodies with "pencil" geometry and intrudes the Nicola Group volcanic sequence. Main stage of mineralization is hosted in Monzonite-A and is cut by Monzonite-D. Alteration is characterized by intense magnetite and K-silicate in Monzonite-A and adjacent volcaniclastics. Monzonite D displays moderate to weak K-silicate alteration. Mineralization is hosted in banded quartz-magnetite-hematite-chalcopyrite veins in Monzonite A and adjacent volcanic host-rocks. SEZ and Deerhorn intrusive units share geochemical characteristics. The early Takomkane units have higher SiO₂ and incompatible element concentrations, less-fractionated HREEs, negative Eu anomalies, and more radiogenic Nd isotope ratios than the Deerhorn monzonites. The latter are themselves similar to the late SEZ FQM which suggests that the latter and the Deerhorn monzonites are co-magmatic. Differences between alteration and mineralization of both deposits are partially attributed to the depth of emplacement; Cu-Au mineralization at Deerhorn represents a shallower expression of the magmatic hydrothermal system and Cu-Mo mineralization in SEZ represents the deeper segment of the partially contemporaneous system. Geochemical and isotopical affinities between the FQM/Monzonite-A/Monzonite-D intrusions and the plagioclase-phyric andesite of the Nicola Group indicate that these intrusions were partially coeval, and that mineralization in the Woodjam area is tightly connected to the Nicola Group volcanism, as age and chemistry of the rocks are similar.

 


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