Prospech Limited (ASX:PRS) has identified rare earths potential with the completion of inspection and sampling of historic drill core from the Korsnäs Project in Finland.
The company recently reached an agreement for the earn-in acquisition of 100% of Bambra Oy, a Finnish company with lithium and rare earth element exploration projects in Finland. These projects are the Jokikangas REE project, the Korsnäs REE project and Saarenkylä lithium project in Finland.
“As historical data is combined with new information from the recent site visit, the possibility of a substantial REE occurrence at Korsnäs is becoming increasingly evident,” Managing Director, Jason Beckton, said.
“The previous Korsnäs mine, which the Korsnäs Project tenure surrounds, primarily produced lead, with only a small amount of rare earth concentrate extracted in its final years.
“Now, the focus is on exploring for REE, and observations from the recent core logging and sampling have revealed that potential zones of REE mineralization were not sampled if there was no obvious association with visual lead (galena).
“The rocks that contain REE are more widely represented in the drilling than the lead bearing ores and both drilling and geophysics suggest that multiple parallel stacked zones of REE mineralization should be targeted.
“The old mine TSF provides a readily accessible REE target that can be relatively quickly explored.”
The Korsnäs REE project consists of exploration licence applications and reservations surrounding the now closed Korsnäs lead mine, which operated between 1959 and 1972. Total mine production was reported as 0.87Mt of ore averaging 3.6% Pb. At the time it was recognized that the mineralization contained allanite and several other REE containing minerals.
Within the Korsnäs Project tenure, core from 60 historic drillholes is stored in the Finnish government GTK core storage facility at Loppi. Prospech’s geologists have examined the core and record data from several holes. During the examination, it was noted that the past core sampling activities had only targeted visibly high-grade lead mineralization, overlooking larger and potentially significant areas of REE mineralized carbonatite.
The company’s geologists have gathered 65 1⁄2-core samples from untested and promising carbonatite sections, which have now been sent to ALS Outokumpu Finland for analysis. Further sampling is planned.
Tailing Storage Facility
The Korsnäs mine operated from 1958 (with first ore production in 1959) to 1972, with the ore being processed on site and tailings being deposited in a dedicated TSF immediately to the north of the mine.
The TSF is approximately quadrilateral and covers about nine hectares, of which approximately 81% is covered by the Korsnäs Project tenement application.
The TSF provides a readily accessible target for exploration. Korsnäs ore processing involved flotation of a lead concentrate with the deslimed lead circuit tailings then being floated to produce a REE concentrate.
GTK records indicate that whereas lead concentrate flotation commenced in 1959, rare-earth concentrates were not produced before 1967, implying that the first 366,000 tonnes of ore were most likely processed prior to the establishment of the REE flotation circuit.
For the remainder of the mine life, REE production from about 504,000 tonnes of ore fluctuated at a recovered grade of about 0.75% REO. A separate published source states the life of mine ore grade as 0.91% La2O3. After mine closure, about 86,000 tonnes of nickeliferous ore from another mine site was also treated at the concentrator, most likely adding to the TSF volume.
The TSF therefore has two target populations. The principal one is the earlier processed lower layer of Korsnäs tailings which may contain grades similar to those recovered from later production. A secondary target will be the REE content in the tailings slimes produced throughout the entire Korsnäs mine life and which were never subjected to concentration.
Prospech’s personnel have taken four grab samples of the tailings from the TSF which have been sent for assay.
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