Samples of the unaltered and altered host rocks at Highland Valley. (a). Unaltered Bethsaida phase with compositions ranging from quartz-monzonite to granodiorite, characteristic rounded quartz phenocrysts, and abundant coarse biotite and plagioclase phenocrysts (ALW-5). (b). Altered Bethsaida phase showing quartz-chalcopyrite-bornite vein with green muscovite alteration halo overprinting earlier K feldspar (pink) alteration (HLV-3b). (c). Weakly altered granodiorite at the margin of the Bethlehem deposit, Highland Valley, with minor secondary biotite after mafic minerals and cut by a thin epidote-chlorite-(sericite) veinlet (BET-1).
Cathodoluminescence images of apatites from unaltered host rocks. (a) Two grains of apatite with uniform yellow and yellow-pale-green luminescence in unaltered Bethsaida granodiorite, Highland Valley (ALW-5). (b). Apatite grains in unaltered Bethlehem granodiorite with a light-brown core, a distinct dark-brown zone and a more green-brown CL at the rim. The smaller apatite grain, in the lower-left side of the photo, shows a similar relationship but with a dark-brown CL in the core as well. Moreover, it shows that the dark-brown zone formed after euhedral crystallization of the apatite. A–B line indicates the profile along which 42 spots were analyzed (BET-1). (c). Apatite from unaltered porphyritic monzonite of the Bootjack Stock, Mount Polley, showing zoned yellow-brown luminescence with a brownish zone (see arrows) occurring in the core and as a narrow zone between the core and rim (PTB042). (d). Apatite from unaltered granodiorite host rocks, Huckleberry, showing zoned brown to orange luminescence (HDM024).
Highland Valley apatite associated with K silicate alteration. (a). Planepolarized photomicrograph showing apatite crystal surrounded by quartz and K feldspar and weakly altered biotite and minor sulfide. (b). Cathodoluminescence image of the same apatite grain showing that the dull yellow-brown apatite is replaced by a brighter green-luminescent apatite at the rims and along fractures. (c). SEM image of the same apatite grain showing no internal structure. Abbreviations: ap = apatite, bio = biotite, chl = chlorite, Kspar = K feldspar.
Cathodoluminescence images of apatites from altered host rocks. (a) Mount Polley apatite occurring with K feldspar + magnetite alteration, showing that green-luminescent apatite has overgrown and locally replaced brown-luminescent apatite (PTB045). (b). Apatite grain occurring with K silicate alteration overprinted by phyllic alteration, showing an early bright green-luminescent apatite cut by dull gray-luminescent apatite. Note that thin green-brown apatite has formed at the rim, presumably after the gray apatite. (c). Huckleberry apatite occurring with K feldspar alteration and sulfide mineralization, showing that brown-luminescent apatite has been replaced by complex bodies of green-luminescent apatite (HDM022-2). (d). Endako apatite occurring with typical K-feldspar alteration, showing dominantly green luminescence with remnant of brown-green-luminescent apatite (EDM 026). (e). Apatite occurring with strong pervasive coarse muscovite and chalcopyrite alteration at Highland Valley, showing that bright green-luminescent apatite is replaced by a variety of dull gray-luminescent apatite phases with fine zoning patterns (ALW-8). (f). SEM image of the above apatite grain showing no internal texture—the very bright phase at the rim and inside the apatite is chalcopyrite (cp), which has formed within a microfracture that has an envelope of green- to gray-luminescent apatite. Acc.V = accelerating voltage (15 Kv), BSE = backscattered electron, Det = detector, Magn = magnification (679×), Spot = refers to specimen current (8–10 nanoamperes), WD = working distance (10.1 mm)
Binary diagram comparing the Mn-Na composition of apatite in the deposits studied with those occurring with felsic and mafic I-type granitoids from the Lachlan fold belt, Australia (Sha and Chappell, 1999). Yellow-luminescent apatite occurs in the felsic I-type field, whereas brown-luminescent apatites occur near, or probably within, the mafic I-type field. DL = detection limit.
Trace element composition of apatite with yellow, green and gray luminescence in unaltered and altered host rocks, Highland Valley, showing that altered samples are depleted in Mn, Na, and Cl. CL = cathodoluminescence, DL = detection limit, pfu = per formula unit
Trace element composition of brown- and green-luminescent apatite at the Mount Polley and Huckleberry porphyry deposits, showing that altered samples are depleted in Na and Cl. CL = cathodoluminescence, DL = detection limit, pfu = per formula unit
Ce, Y, and Nd concentration in various types of apatite occurring with unaltered and altered host rocks at Highland Valley. Note that unaltered yellow CL apatite with weak green luminescence has slightly lower REE concentration. Other REE show similar trends. CL = cathodoluminescence.
Chondrite-normalized REE distribution patterns of apatites from Highland Valley granodiorite in normal scale (a) and log scale (b), showing that altered samples are characterized by strong REE depletion and weaker Eu anomaly. Samples with strong phyllic alteration display a flat REE with erratic LREE pattern. Chondrite REE abundances are from Sun and McDonough (1989).
Correlation of the apatite luminescence and alteration with the Mn/Fe ratio and abundance of REE. Very weak K silicate alteration of apatite occurs as slightly green-, yellow-, luminescent apatite. The pale green-yellow luminescent apatites have slightly but distinctly lower REE. K silicate-altered samples, have green luminescence, and a lower REE and Mn/Fe ratio. Sericite-altered apatites have gray luminescence and lowest REE and Mn/Fe.
Binary diagram showing correlation of the apatite luminescence and alteration with the concentration of Na2O and SO3. K silicate-altered samples have lower Na and S. CL = cathodoluminescence, DL = detection limit, pfu = per formula unit.