Mine tailings dumps at the Kalengwa copper project in Zambia have yielded an average grade of 1.03% copper and 4.44 parts per million silver, with copper values ranging from 0.59% to 2.48%, according to assay results from preliminary sampling by resource, development and mining company Xtract Resources.

Xtract executive chairperson Colin Bird said in a statement released last month that the result confirmed copper grades in tailings over a large sample population, similar to results reported in the 2013 resource estimate for the Kalengwa copper project, in the North-Western province, 800 km north-west of Lusaka and 400 km south-west of Kitwe.

The Kalengwa mine operated in the 1970s and was one of the highest-grade copper deposits in Zambia, says Xtract.

Historical mining and processing operations at the high-grade Kalengwa copper mine generated tailings that were contained initially in a tailings storage facility, reportedly 6 m to 8 m deep. Later tailings were deposited directly into an adjacent swamp. Periods of poor concentrator recovery at the mine resulted in relatively high-grade copper material being sent to tailings, according to a 2013 report by previous site operator Lunga Resources.

The historic tailings resource of about two-million tons averages 1.02% copper, indicating total copper content of 20 300 t, with some silver by-product. The resource was reported in 2013 and is noncompliant with a recognised standard and has, subsequently, not been updated or verified.

In July this year, Xtract undertook its preliminary confirmatory sampling programme along three hand-dug trenches totalling 420 m. Two trenches were dug in the main tailings facility, while a third was dug in the swamp area. Trench depths ranged from 1 m to 3.5 m.

Xtract collected 93 samples, about every 5 m along the trenches, by sampling vertical channels from top to bottom at each location. The sampling was planned to represent average sample values over a period during the historical mining operation. Sample weight was generally 2 kg to 3 kg.

All samples were submitted for analysis to testing laboratories company SGS’s Kalulushi geochemical laboratory, in Zambia, which is ISO/IEC 17025 accredited for copper analysis.

“We are undertaking metallurgical testwork to assess the optimal method for [copper/silver] recovery through mineral processing, upgrading or separation at site. Work is continuing at Kalengwa to enhance local infrastructure to facilitate the planned operation,” noted Bird in the statement.

In the near term, Xtract intended to undertake drilling to assess primary ore potential to the north and south of the former openpit, he added.

On April 2 this year, Xtract's partner, mineral explorer KPZ International, was issued large-scale exploration permit 24401-HQ-LEL, which is initially valid for four years.

On July 15, 2019, Xtract announced the conclusion of a memorandum of agreement with KPZ, naming Xtract as the contractor for the Kalengwa processing project.

The Kalengwa copper mine was owned and managed by Roan Consolidated Mines from 1970 to 1982. Total production of 1.9-million tons of 9.44% copper and 50 g/t silver was achieved through openpit mining, resulting in about 15 000 t/y of copper being produced over 12 years.