Three different albite pods were sampled in order to understand the corresponding mineralogical and chemical variations from the most albitized portions of the albite pod, to the least altered portions. Albite Pod #3 was the first albite pod to be sampled (Figure 3.3 in Chapter 3) and contains seven sample blocks. Figure 4.36 shows the variable degrees of alteration within Albite Pod #3. Figure 4.36 (a) is a fairly fresh, coarse-grained ophitic gabbro with primary plagioclase, clinopyroxene and magnetite. In Figure 4.36 (b), Block 3 is also coarse-grained, but contains significant albite, actinolite and chlorite alteration. Block 5 in Figure 4.36 (c) shows very weak alteration, is medium-grained, and contains a primary assemblage of plagioclase, clinopyroxene and magnetite. Finally, Block 7 in Figure 4.36 (d) is fine-grained and contains moderate albite and actinolite alteration that is pseudomorphic after plagioclase, and clinopyroxene respectively.
Albite Pod #5 contains patchy, sporadic albite alteration that is very strongly spatially associated with actinolite alteration within all seven sample blocks taken during a transect of the Albite Pod (shown in Figure 3.4 in Chapter 3). A progressive sequence of sample blocks shown in Figure 4.37 demonstrates the extent of alteration that is present within every other block. The main alteration assemblage includes dirty-brown texture albite, intergrown with deep green actinolite that is pseudomorphic after plagioclase and
clinopyroxene respectively. Medium to fine-grained apatite is common within the sugary- textured albite. Figure 4.38 (a) and (b) show unaltered portions of Blocks 1 and 3 within Albite Pod #5. The unaltered portions contain roughly equal proportions of plagioclase and clinopyroxene, with lesser magnetite. The amount of alteration present within Blocks 1 to 7 is variable and sporadic. The style of mineralization within Albite Pod #5 is
constrained to small blebs and disseminations of chalcopyrite that are spatially associated with euhedral to subhedral actinolite (Figure 4.38 c & d).
The Discovery Outcrop Albite Pod contains a very progressive order of most altered sample (Block 1), to the least altered sample (Block 8). This progression of alteration is summarized in Figure 4.39, where the general textures of Blocks 1, 3, 5, and 7
alteration is pervasive, albite and actinolite alteration completely overprint the primary mineralogy. This is observed within Blocks 1 and 3 in Figure 4.39 (a) and (b). Where alteration is less significant, the primary mineralogy includes plagioclase, clinopyroxene, skeletal olivine, skeletal magnetite, and apatite. Despite the level of alteration changing gradually from Block 1 to Block 8, the amount of copper and platinum group element mineralization does not correspond to the degree of alteration.
Figure 4.36 – A) A photomicrograph in PPL showing the general texture of Block 1. There is limited alteration, but when present, it is manifested as dusty mantling of plagioclase laths, and thin biotite rimming of magnetite grains. Overall grain size is coarse, B) A photomicrograph in PPL showing the general texture of Block 3. Alteration is quite strong, and is exhibited by strong (dirty brown) albite alteration of plagioclase, in addition to green pseudomorphic actinolite alteration of clinopyroxene. Grain size is coarse. C) Another photomicrograph in PPL which shows the general texture of Block 5. There is slight albite alteration of plagioclase rims, and thin biotite rims have formed around magnetite grains. However, overall, the primary igneous texture is very little disturbed. D) A photomicrograph in PPL showing the general texture of Block 7. Grain size is fine, and alteration is prevalent in the form of pseudomorphic actinolite alteration of clinopyroxene, as well as partial to complete albite alteration of plagioclase, and biotite alteration of magnetite rims.
Figure 4.37 – A to D) Photomicrographs in PPL showing the general texture of sample Blocks #1, #3, #5 and #7 within Albite Pod #5. The alteration mineral assemblages are all similar within all these various blocks, including primarily albite and actinolite that are pseudomorphic after plagioclase, and actinolite respectively. The proportion of albite to actinolite is relatively constant from block to block.
Figure 4.38 – A to B) Photomicrographs in PPL showing the texture of the unaltered portions of Block #1 and #3 in Albite Pod #5. Plagioclase shows slight mantling of albite, which clinopyroxene shows slight alteration to actinolite at the margins of fractures, C) The mineralization style observed in Albite Pod #5 in PPL, where actinolite grains are clustered together, and are euhedral, surrounding interstitial chalcopyrite, D) The same image as in (C), but in reflected light showing chalcopyrite interstitial to actinolite.
The sulfide mineralization within the Discovery Outcrop Albite Pod is quite different from anywhere else documented within the Geordie Lake deposit. The most common sulfide assemblages within the Discovery Outcrop Albite Pod include that of
chalcopyrite, bornite, and covellite with lesser pyrite, and less commonly pentlandite, sphalerite, and galena. Figure 4.40 shows the associations of chalcopyrite to magnetite, bornite, and covellite. All bornite within these particular samples exhibit strong
Widmanstatten textures with faint chalcopyrite lamellae. In Figure 4.40 (a), Coarse-
Figure 4.39 – A) A photomicrograph in PPL showing the general texture of sample Block #1 in the Discovery Outcrop Albite Pod. The mineralogy is dominated by mainly albite, and actinolite that is pseudomorphic after clinopyroxene, B) A photomicrograph in PPL which shows the general texture of Block #3 in the Discovery Outcrop Albite Pod. Alteration is still quite pervasive, featuring mainly cloudy-brown, saccharoidal albite pods along with patches of actinolite. Actinolite is commonly intergrown with chalcopyrite, which also occurs adjacent to the albite pods, C) Photomicrograph of Block #5 in the Discovery Outcrop Albite Pod in PPL. A dark brown albite bleb fills in heavy fractures within a clinopyroxene grain, and is intergrown with fine grained actinolite. Clinopyroxene in this sample is, overall, quite unaltered, D) A photomicrograph in PPL of the general texture within sample Block #7 in the Discovery Outcrop Albite Pod, showing that the overall texture is quite unaltered, particularly relative to the other blocks within the Discovery Outcrop Albite Pod. Ophitic textures are created by euhedral plagioclase and interstitial clinopyroxene
grained magnetite (with ilmenite exsolution lamellae) contain inclusions of chalcopyrite. Chalcopyrite primarily occurs at the rims and within fractures of magnetite in this reflected light image. In Figure 4.40 (b), chalcopyrite and bornite occur in proximity to magnetite. Bornite grains are rimmed by covellite. Figure 4.40 (c) shows a grain of chalcopyrite with actinolite inclusions, and bornite exsolution. This chalcopyrite grain is hosted within a larger magnetite grain. Figure 4.40 (d) shows the Widmanstatten texture exhibited by bornite, which contains chalcopyrite lamellae. Fractures within this bornite grain are rimmed by covellite.
Figure 4.40 – A) A reflected light image of one mineralization style observed within the Discovery Outcrop Albite Pod sample blocks. A coarse grained magnetite grain contains fine grained inclusions of chalcopyrite, which contains even finer grained bornite exsolution, B) A reflected light
photomicrograph which shows a large grain of bornite intergrown with chalcopyrite. The rims of the bornite grains are altered to covellite (in blue), C) Photomicrograph in reflected light of a large chalcopyrite grain, with abundant bornite and covellite intergrowths. As in (B), covellite tends to be associated with the fracture planes of the chalcopyrite grain. The large chalcopyrite grain is completely enclosed by magnetite. A pyrite grain occurs at the right margin of the chalcopyrite grain, presumably as an alteration mineral. D) A reflected light image close-up of bornite within the Discovery Outcrop Albite Pod. Bornite tends to exhibit thin lamellae of chalcopyrite in a Widmanstatten pattern