Following alluvial exploration activities undertaken in 2021, ASX-listed Lucapa Diamond Company and its partners have increased the Angola-based Lulo mine’s diamond resource in situ carats by 11%, from 135 900 ct as at December 31, 2020, to 151 040 ct at December 31, 2021, after accounting for mining depletion of 24 595 ct during the 2021 calendar year.

Lucapa, along with its partners – 40% Lucapa-owned mine operator Sociedade Mineira Do Lulo (SML), Angolan national mining company Empresa Nacional de Diamantes (Endiama) and private Angolan company Rosas & Petalas – announced the exploration results on March 28.

“Notwithstanding the increase in mining capacities over the last seven years by SML, this is the fourth consecutive year in which the resource carats have increased,” the company said in a statement.

The updated Joint Ore Reserve Committee classified inferred alluvial diamond resource was independently estimated and reconciled on a depletion and addition basis to December 31, 2021, by external consultants Z Star Mineral Resource Consultants of Cape Town.

The updated Lulo diamond resource was estimated after taking into account the delineation of new or additional resources and improved knowledge of existing resource areas through extensive auger drilling of about 7 000 holes and about 1 500 hole pitting programmes.

The sales of diamonds produced during 2021 was also taken into account, totalling $78.1-million at an average diamond price of about $2 808/ct.

Lucapa said diamond valuations had been significantly affected by the steep recovery in the diamond market during 2021 and early this year. The modelled diamond value model has, therefore, been escalated using a global rough diamond price index provided by independent diamond valuation consultancy GTD Consultants up to December 31, 2021.

The company further stated that, since 2020, modelled diamond values have increased by about 34% from $1 440/ct to $1 930/ct on average.

The total diluted volume of gravel available for mining in the updated Lulo diamond resource also increased to 2.2-million cubic metres. This equated to a minimum of four years of resource at SML’s expanded mining and processing capacities, Lucapa said.