Grotto Group, Omineca Mining Division, British Columbia, Canadai

Regional Level Types
Grotto Group	Occurrence
Omineca Mining Division	Mining Division
British Columbia	Province
Canada	Country

The Grotto Group occurrence is located about 40 kilometres north-east of Terrace, British Columbia, on either side of Hardscrabble Creek, approximately 1.8 kilometres north-west of the creek mouth on the Skeena River.
The following quote is from B.C. Government site “Minfile”- Minfile No. 103I 045, current to 2015:
“The area is underlain by andesites of the Jurassic Hazelton Group, which have been intruded by porphyritic granodiorite dikes and stocks of the Cretaceous to Tertiary Coast Plutonic Complex.
Narrow quartz veins and stringers occur adjacent to contacts of the dikes and stocks and along shears and faults in the andesites. Mineralization consists of pyrite, chalcopyrite and specularite, with minor amounts of sphalerite, petzite, hessite, cosalite, empressite, rickardite, chalcocite and possibly native tellurium.”
Comments by Giles Peatfield regarding some of the minerals reported:
Azurite: Godwin (1962) reported azurite as a surface alteration product.
Bornite: Kindle (1937) reported bornite, and Godwin (1962) found it in polished section.
Chalcocite: Duffell and Souther stated that chalcocite had “been reported”, but gave no details; it was also reported by Bysouth (2012). I regard it as tentative.
Cosalite: This was reported only by Mandy (1939), with no supporting data. I regard it as tentative.
Covellite: Godwin (1962) reported covellite with chalcopyrite in polished section.
Empressite: Empressite at Grotto requires some explanation. Thompson (1954) described empressite – it is not fully clear from his paper, but it appears that he also described a similar mineral, with a brown tarnish, which he X-rayed and found to give a similar pattern to that of Empressite? (material 4) of Thompson, et al. (1951). The two “empressites” – Empressite I and Empressite II – were listed with powder patterns in Berry and Thompson (1962). Godwin (1962), working under the direction of Thompson at UBC, described two minerals – empressite, which he said was “Previously identified by X-ray techniques.” (presumably by Thompson?), and a second mineral “Not distinguishable from empressite in the polished section. Previously identified by X-ray techniques.” The question remains – if he could not distinguish it from empressite, how did he know it was different? Presumably Thompson told him so, but we will never know. Finally, Scott (1971) reported empressite from Grotto. Dr. Scott has informed me (personal communication Feb. 2022) that he has a small chip from a larger specimen, now sadly lost, from which he obtained an X-ray pattern identical to that of Berry & Thompson’s “Empressite I”, now known to be stützite. Readers interested in following the “empressite” story should refer also to Honea (1964) and Stumpl and Rucklidge (1968). The best that can be said here is that empressite (sensu stricto) may occur at Grotto; stützite certainly does.
Gold: Scott (1971) stated that native gold had been reported in polished section. In a recent personal communication (Feb. 2022), Dr. Scott says he was not the one who recognized gold, and does not know who did. Given the gold grades reported, I am sure that it exists here and is valid for the locality.
Hematite: Bysouth (2012) reported “black hematite” in addition to the more common specularite.
Hessite: This has been reported by several workers, most notably Mandy (1939) who gave no supporting data. In his examination Godwin (1962) did not see hessite in polished section, but described a black, sectile tarnish which yielded a positive microchemical test for copper and tellurium; he thought this was probably hessite, but given the copper test one must be suspicious.
Malachite: Godwin (1962) reported malachite as a surface alteration product.
Petzite: Several workers have reported petzite, with no supporting data, but Godwin (1962) was not sure, and reported it as “probable” only.
Pyrrhotite: This has been reported by Bysouth (2012), but is certainly not common at Grotto.
Rickardite: This was reported, and presumably X-rayed, by Thompson (1954). Thompson’s student Godwin (1962) identified rickardite, stating that it was “Previously identified by X-ray technique.”, presumably by Thompson.
Stützite: For this, refer to the comments for Empressite (above).
Tellurium: This has been reported by several workers at Grotto; Godwin mentioned that it had been previously X-rayed.

References

Other Databases

Link to British Columbia Minfile:	103I++045

Other Regions, Features and Areas containing this locality