Rayfield copper prospect, Rayfield River, Clinton Mining Division, British Columbia, Canadai

Regional Level Types
Rayfield copper prospect	Deposit
Rayfield River	- not defined -
Clinton Mining Division	Division
British Columbia	Province
Canada	Country

The Rayfield copper prospect is located near the headwaters of Rayfield River, about 42 kilometres north-east of Clinton, and 88 kilometres north-west of Kamloops, British Columbia, in the Clinton Mining Division.
There is an extended description of the property on the British Columbia “Minfile” site, current to 2019, to which interested readers are referred. Relevant portions pertaining to geology are quoted below:
“Regionally, the area is underlain by several phases of a concentrically zoned, probably Late Triassic to Early Jurassic, syenitic to monzonitic to dioritic plutonic complex. The complex occurs as a window through Miocene to Pleistocene alkaline plateau basalts of the Chilcotin Group, which blanket much of the Cariboo Plateau. The core of the complex consists of leucosyenite composed almost entirely of alkali feldspars with 1 to 3 per cent amphibole and trace amounts of white mica, magnetite and quartz (Assessment Report 2135 [Hodgson et al. 1969]). Syenite pegmatite dikes are common, with feldspar making up more than 95 per cent of the rock. Other less common syenite pegmatites contain minor amphibole minerals, less common nepheline and rare quartz.
Locally, prospecting and sampling has identified visible low-grade copper mineralization, between 0.05 per cent and 0.1 per cent copper, over an area of approximately 600 by 2500 metres. Mineralization consists of bornite and chalcopyrite, largely altered to malachite, occurring in feldspar (alteration?) veinlets and fracture fillings and as disseminations replacing mafic minerals and blebs up to 3 millimetres in size associated with syenite pegmatite dikes. Chalcocite, cuprite and native copper mineralization have also been reported. The most widespread veinlet set is sheeted, trending north-northwest and dipping 40 to 60 degrees west. Alteration minerals include potassium feldspar, epidote, chlorite, sericite and hematite.”
Logan and Schiarizza (2014) reported several radiometric dates for the Rayfield River pluton; see their paper for details. In summary, two earlier K-Ar dates (hornblende - 193±14 Ma and biotite - 186±12 Ma) give a minimum age for the hornblende syenite unit (see rock section below for explanation of lithologies). U-Pb zircon ages for the same unit were reported as 198.6±0.4 Ma and 200±0.4 Ma, while zircon from a later monzogranite dike rock yielded preliminary results of 199.7 - 199.9 Ma. The plutonic complex is thus dated as earliest Jurassic.
There are no reports of calculated mineral resources for the Rayfield copper prospect. Pilcher and McDougall (1976) quoted “0.1% Cu (2300 x 660 m) within 0.05% Cu 4000 x 1600 m, Au values ?”, referencing GEM 1970 [Preto, 1971]. The prospect, as presently known, is clearly sub-economic. Of interest is that the available gold analyses for the prospect are very low, leading Logan and Schiarizza (2014) to comment that “Copper grades reported from historical work (surface trenching and diamond drilling programs) average between 0.05 - 0.1% Cu and < 50 ppb Au (Selmer [sic - Sellmer] et al., 1968; Hodgson et al., 1969; Preto, 197[1]; Wynne, 1990; Koffyberg, 2008). Gold values are typically less than 10 ppb, and although elevated gold values accompany higher grades of copper, the Cu:Au ratios are several orders of magnitude below the 1:1 (1 g/t Au to 1% Cu) suggested for gold-rich porphyries (Kirkham and Sinclair, 1995) and the ranges for British Columbia alkaline deposits (Panteleyev, 1995).”
The Rayfield copper prospect is included in the USGS compilation by Singer et al. (2008). The information given by Singer et al. (2008) is incomplete.
Giles Peatfield comments on the minerals reported:
The following comments, derived from several reports, give some details of the various minerals reported from the Rayfield copper prospect and immediately surrounding area. These comments are by no means exhaustive. There are a few points of specific interest. There are no reports of molybdenum mineralization, and such assay data as are available show, in most cases, values of less than 10 ppm Mo. Wynne (1990) reported, in his drill core logging, numerous examples of “realgar?” and a few of “cinnabar?”. Again, search of available drill core assays show very low to negligible levels of As and Hg, thus putting the putative occurrence of these two minerals into question. Finally, Singer et al. (2008) list marcasite, but it is not clear who made the identification. I can find no other references to marcasite here, and regard it as tentative at best.
Amphibole group: Most workers simply reported “hornblende” with no further details. Le Couteur (2007), however, describing the amphibole in a thin section of “amphibolitized syenite” noted that based on microprobe data “The amphibole is a calcic amphibole, probably of the Fe-Mg hornblende series.”
Apatite: This has been reported by several workers. Le Couteur (2007) presented photomicrographs with c. 0.1mm euhedral apatite crystals in syenite and blocky crystals up to 0.3mm in “amphibolized” syenite.
Azurite: Although not unexpected, this has only been reported by Tupper and Tupper (2015) as “occasional” with malachite.
Bornite: This is common, reported by most workers as fine disseminations. Logan and Schiarizza (2014) consistently refer to bornite grains as “blebs”.
Calcite: This is a relatively minor constituent of the syenitic rocks, occurring as late stage veinlets.
Cancrinite: Logan and Schiarizza (2014) noted that “Pegmatites in the hornblende syenite contain coarse (up to 5 cm) tabular microcline (65-80%), interstitial (1-2 cm) equant plagioclase (15-30%), and minor nepheline, cancrinite, corroded pyroxene and/or hornblende, biotite, titanite, calcite and sericite.”
Chalcocite: This is a minor constituent of the copper mineralization. Logan and Schiarizza (2014) noted that “Secondary supergene chalcocite, malachite, and rare native copper are associated with altered fault zones and surface weathering.”
Chalcopyrite: This is principal copper mineral of economic importance, reported by all workers, generally as finely disseminated grains.
Chlorite group: Most workers reported “chlorite”, or “chloritization”, or “chlorite alteration”, but none gave any specific mineral data.
Copper: Native copper, in some cases as dendritic growths, was noted by Wynne (1990) in drill core logging.
Covellite: The only reference to covellite was by Logan and Schiarizza (2014), who described a “Plane polarized reflected light photomicrograph of [a] mineralized vein cutting hornblende syenite . . . . Bornite vein is enveloped by pale green epidote and contains chalcopyrite exsolution lamella. It is replaced along curved fractures by chalcopyrite and covellite.”
Cuprite: This is somewhat problematic. Both Wynne (1990) and Koffyberg (2008) report numerous occurrences in the course of core logging, but often they both refer to “cuprite?” as if they are not sure of the identification. Both also note the putative mineral at considerable depths, admittedly in fault zones. I am prepared to accept the occurrence of cuprite as valid here but advise caution.
Epidote: Most workers noted traces of epidote, generally as a late stage alteration product.
Feldspar group: Several varieties of feldspar have been reported in the syenitic rocks at Rayfield. Preto (1971), presumably based on thin section analyses, reported “sodic plagioclase”, “perthite” and “microcline microperthite”. Le Couteur (2007) reported “orthoclase”, “albite”, “albite-oligoclase” and “perthitic orthoclase”. Logan and Schiarizza (2014) reported “microcline microperthite”, “sodic plagioclase”, “orthoclase” and “perthitic microcline”.
Garnet group: There is some uncertainty here. Hodgson et al. (1969) reported “melanite garnet”; Preto (1971) reported simply “garnet”; and Le Couteur (2007), in examination of a sample of syenite, wrote that “A dark brown mineral encountered only in the stained off-cut . . . was analyzed . . . , and appears to be andradite.”
Hematite: This is common, often as an alteration of magnetite (Le Couteur, 2007) or on faults and fractures (several workers).
Limonite: Although limonite is probably common, there are few direct reports. Wynne (1990) noted it in core logging; Tupper and Tupper (2015) reported “iron oxide” staining.
Magnetite: This is common, reported by most workers. Le Couteur (2007) described it in several polished sections as partially replaced by hematite.
Malachite: This is common, reported by several workers.
Mica group: Most workers have reported “biotite”, “sericite (or white mica)” or “muscovite”. Le Couteur (2007), describing a thin section of syenite, wrote that “Aggregates of fine-grained muscovite (30%) fill interstices between the feldspars . . . and consist of masses of flakes 0.01 to 0.2 mm long, with a smaller amount of coarser grains to 0.5 mm across . . . . It appears from other samples in this set that the fine-grained mica masses replaced primary plagioclase feldspars, which initially made up probably 20%, while the coarser muscovite appears to be a primary constituent.” Le Couteur (2007) also noted numerous examples of brown and green biotite, often partially replaced by chlorite. Logan and Schiarizza (2014) noted that plagioclase feldspars are in many cases altered in whole or in part by sericite.
Nepheline: This was reported by, amongst others, Preto (1971) who commented that it had been confirmed in thin section and by X-ray analysis.
Pyrite: This is problematic. Sellmer et al. (1968) commented that “Pyrite is conspicuously absent.” This statement was echoed by several workers, most notably Logan and Schiarizza (2014), who also noted that “Hematite occurs throughout the syenite, and pyrite is conspicuous by its absence.” However, both Wynne (1990) and Koffyberg (2008) noted numerous minor occurrences in drill core. Possibly other workers were dealing with surface rocks where pyrite had been destroyed by weathering. I am prepared to accept the occurrence of pyrite as valid here but advise caution.
Pyroxene group: Hodgson et al. (1969) wrote that in the amphibole syenite “Accessory minerals include brown biotite, augite (relict centers to some amphibole crystals), . . .” Preto (1971) described “. . . minor amounts of corroded pyroxene grains . . . .” Logan and Schiarizza (2014) reported corroded pyroxene grains in syenites, and in the overlying Quaternary basalt they noted both clinopyroxene and orthopyroxene but did not give specific mineral names.
Quartz: This is not a common mineral at Rayfield River. Logan and Schiarizza (2014) reported it as a constituent of late-stage quartz-feldspar porphyry dikes. Wynne (1990) noted numerous examples of thin quartz-bearing veinlets in drill core.
Titanite: Le Couteur (2007) reported 1mm to 2mm grains, generally euhedral, of titanite in syenites. Logan and Schiarizza (2014) reported numerous examples of titanite in syenites. Earlier workers (Hodgson et al. 1969; Preto 1971) reported “sphene” as an accessory mineral in syenitic rocks.
Zircon: Le Couteur (2007) reported zircon in a thin section of a coarse-grained syenite. Logan and Schiarizza (2014) noted that zircon grains were used for radiometric dating.
Giles Peatfield comments on the rock types reported:
The rock types listed are taken from several reports. I have chosen to comment individually on the various units.
Basalt: This occurs in the form of mafic dikes or the overlying Quaternary lavas, reported by Sellmer et al. (1968), Preto (1971), Koffyberg (2008) and Logan and Schiarizza (2014).
Diorite: This rock, described by numerous workers, is part of the Rayfield plutonic suite. Preto (1971) commented that “It contains nearly equal amounts of potash feldspar and of strongly sericitized plagioclase with about 20 per cent dark-green amphibole and olive-brown biotite, and is thus more properly termed a monzonite.”
Hornblende syenite: This rock is also called, by several of the workers, “amphibole syenite”; it is one of the principal units of the Rayfield plutonic suite.
Leucocratic syenite: This rock, also called “leucosyenite”, is another major unit of the Rayfield plutonic suite.
Monzonite: See comment above for diorite.
Pegmatite: Also called “syenite pegmatite” or “pegmatitic syenite” is common in relatively restricted bodies. Logan and Schiarizza (2014) wrote that “Pegmatite is common as irregular pods and dike-like masses concentrated around the leucosyenite, but is also in the hornblende syenite throughout the pluton.”
Quartz feldspar porphyry: Logan and Schiarizza (2014), describing dike rocks, wrote that “The hornblende syenite and leucosyenite units are cut by north-northwest-trending dikes that include, in decreasing order of abundance, pegmatite, syenite, orthoclase porphyritic quartz monzonite, and quartz-feldspar porphyry.”

Giles Peatfield
BASc. (Geological Engineering) University of British Columbia 1966.
PhD Queen's University at Kingston 1978.
Worked for Texas Gulf Sulphur / Texasgulf Inc. / Kidd Creek Mines - 1966 to 1985.
Vancouver based consultant 1985 to retirement in 2016

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Link to British Columbia Minfile:	092P 005

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References