Base Metals Deposits

Petrographic and cathodoluminescence studies provide important information for exploration and deposit characterization:

  • Identification and distribution of ore mineralogy
  • Characterization of alteration and zonation patterns
  • Identification of episodes of Q veining and Kspar metasomatism
  • Textures of ore and gangue minerals and their effect on metallurgical extraction
  • Distribution of key gangue mineral phases
    •
    Identification and distribution of ore mineralogy (RL)
    The ore mineral assemblage in the porphyry breccia in the left photo includes molybdenite and chalcopyrite rimmed with digenite. The porphyry mineralization in the right-hand photo consists of chalcopyrite lamellae in bornite and patches of covellite and digenite.
    Characterization of alteration and zoning (CL)
    Two Ksp-altered breccias from the Copper Creek district of Arizona. The breccia on the left contains only weak Cu mineralization (<0.5% Cu). Both primary igneous Ksp and late magmatic metasomatic Ksp in this breccia have light blue luminescent Kspar. The breccia in the right-hand photo is high-grade (>1% Cu). Ksp in the host aplite porphyry and early A-vein selvages have light blue CL. Hydrothermal Ksp3 accompanies strong chalcopyrite mineralization. The hydrothermal Ksp has brown CL and occurs as breccia matrix and as replacement of plagioclase phenocrysts. Magmatic and A-vein quartz has dull blue CL, while hydrothermal quartz is non-luminescent.
    Characterization of alteration and zoning (CL)
    Two high-grade Cu porphyry breccias from the Copper Creek district, Arizona. The bx in the left hand photo has massive chalcopyrite (identified in the photo by embedded green CL polishing media), drusy brown Ksp3, and non-luminescent quartz (Q3) filling space between host aplite porphyry blocks. Primary quartz (Q1) as phenocrysts and in porphyry matrix has dull blue CL. Primary Ksp (Ksp1) in aplite matrix has light blue CL. Brown CL hydrothermal Ksp3 also replaces plagioclase in the porphyry blocks. The matrix of the bx in the right-hand photo contains yellow CL apatite , red CL dolomite replaced by green CL carbonate, brown CL Ksp3, pink CL anhydrite, and specularite needles. Veinlets with Ksp3-Q3-cp crackle host rocks to about 60 m beyond the breccia margin and provide an exploration tool for high-grade breccias in the district.
    Application to a variety of sample types (CL)
    The cathodoluminescence (CL) technique is applicable to a variety of sample types, including polished sections and thin sections, unpolished thin sections without cover glass, unprepared chips and cut slabs, metallurgical concentrates, RVC drill chips, and stream sediments.