The story “Junior eyes rare-metal pegmatite” (T.N.M., May 31-June 6/99) by John Cumming contains a number of inaccurate and misleading statements calculated to cause confusion among your readers.
- Contrary to the photo caption and subsequent description, no primary petalite has been observed in the Pakeagama pegmatite. This is clearly stated in Ontario Geological Survey Miscellaneous Paper No. 169, the main reference for the story, in which Dr. Fred Breaks observes that any primary petalite originally contained in the pegmatite has long since been converted to SQUI (spodumene-quartz intergrowth), as is the case with the Tanco pegmatite in Manitoba. Preservation of primary pegmatite is an unusual phenomenon which, at this point, is unique in North America to the pegmatites of the Separation Rapids area.
- Dr. Breaks also clearly states, in the same publication, that the width of the pegmatite varies from 10 to 30 metres, not 10 to 70 metres as reported by The Northern Miner and Houston Lake Mining. This is also evident from the map included in that report.
- The only definitive indicator of potential for economic tantalum mineralization in a rare metals pegmatite is ore-grade tantalum assays from a systematic sampling program. No tantalum assays of any kind are reported for Pakeagama Lake by either Houston Lake Mining or the Ontario Geological Survey. In fact, Dr. Breaks describes the oxide minerals (including tantalum phases) as “typically fine-grained and sparsely evident in the zones observed to date.”
- I remind The Northern Miner that the use of the term “deposit” to describe the pegmatite occurrence implies that a resource has been delineated. This requires systematic sampling by trenching and drilling, neither of which has been carried out to date at Pakeagama Lake.
In light of the recommendation of the Mining Standards Task Force, any Qualified Person will tell you that the Pakeagama Lake pegmatite requires much more exploration work before it can ever be described as a “significant deposit.”
Economic rare metal deposits are very rare. Pakeagama Lake represents an interesting new occurrence of rare metal mineralization (one of many in northwestern Ontario), providing further evidence of the potential for this type of deposit in the province.
Donald Bubar
Unionville, Ont.
Author John Cumming responds:
- The Pakeagama Lake pegmatite does belong to the petalite-subtype group of pegmatites. However, the petalite appears to have broken down into intergrowths of quartz and the lithium-ore mineral spodumene, which has a higher value than petalite.
Grayme Anthony, president of Houston Lake Mining, states: “We want to put forward the fact that we have significant tantalum and cesium potential. We prefer to stay away from the term “petalite,” other than referring to its genetic name, because we don’t want to be in competition with Avalon Ventures on the basis of petalite. I’m basically cheering for Avalon to go ahead, because it brings attention to the sector.”
- In a later summary of his work prepared for Houston Lake, Breaks describes the width of the Pakeagama Lake pegmatite as ranging from 10 to 70 metres. Furthermore, he states: “The pegmatite widens at its northwestern and southeastern outcrop limits. [It] appears to be expanding in width especially at the southeastern limit of exposure where a width comparable to the Big Whopper pegmatite is obvious.”
- While ore-grade tantalum assays are preferred, variations in chemical composition can also play a role in determining the economic potential of rare-metal pegmatites. Breaks states in his Pakeagama report: “A well-defined trend of chemical evolution, expressing a change from mangano-columbite into mangano-tantalite is obvious (in the Pakeagama Lake pegmatite). . . Such evolutionary trends indicate a high potential for tantalum-rich zones in the pegmatite system.
“An absence of relatively primitive ferro-columbite compositions in the Pakeagama Lake pegmatite is also notable, and supports the high exploration potential for tantalum.”
- Strictly speaking, a deposit should have a tonnage and grade figure attached to it, but the article makes clear that exploration at Pakeagama Lake is at its earliest stages. However, in a geological sense, the Pakeagama Lake pegmatite system is undeniably large, having been traced and sampled on surface for over 250 metres. As for the pegmatite’s significance, Breaks writes: “It is now clear that [it] represents the second-largest complex-type, petalite-subtype pegmatite in Ontario, being surpassed only by the Big Whopper pegmatite in the Separation Lake area.”
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