Diamond resources, reserves and price-driven re-evaluations, 2021–2026
Asked (summary):
How have diamond deposits' resource and reserve estimates changed over the past five years — their technical and geological parameters — and did mines and projects re-evaluate their reserves or resources because of the recent drop in diamond prices?
The evidence covers 60 sourced records from 43 independent hosts: 21 recent project resource/reserve estimates, 24 documented resource or reserve changes, and 15 market-context records dated 2021–2026. It is a broad documented sample, not a complete census of every diamond deposit — several jurisdictions and private or state operators publish no comparable current technical reports.
What actually moved each estimate
Every documented resource or reserve change, placed by its effective or report date and grouped by its stated mechanism. Only three changes are explicitly price-linked in the sources; most carat movements are geological or technical. Hover or tap a diamond for the before/after amounts and the stated cause. Flagship cases are labelled.
Karowe's underground reserve fell about 30%, from 5.2 Mct to 3.7 Mct, as lower modelled prices made marginal ore unprofitable and the north and centre lobes (~170,000 ct) were removed — one of the few explicitly price-linked reserve cuts. aidi.org
Petra booked impairments at Cullinan (US$70m) and Finsch (US$37m) driven largely by revised forward diamond-price assumptions, while its gross resources slipped from 142.25 to 140.51 Mct and 34.32 to 33.32 Mct with no stated cause — price hit value, not clearly carats. minedocs.com
Letšeng's life of mine was cut from 2039 to 2035 under current pricing assumptions, waste mining was reduced 46% and deferred, and a US$10.7m goodwill impairment taken — economic re-evaluation without a price-attributed carat change. sharecast.com
The market backdrop was severe: rough prices fell roughly 30–40% from their 2022 highs on weak Chinese demand, inventory gluts, lab-grown substitution and tariff disruption, and producers cut output, capex and mine plans in response. kivalliqnews.com
The mechanism: how a price fall erases reserves but not rocks
Lower price → lower revenue per tonne → marginal material excluded
A lower diamond-price assumption cuts the modelled revenue factor of each block, shrinking the economic pit shell or raising the cut-off. Marginal tonnes and carats are excluded or deferred, so Mineral Reserves — the economically mineable part — can fall, mine lives shorten and waste stripping is deferred, while the geological Mineral Resource may stay unchanged or even grow with new drilling. Karowe (reserve cut, lobes removed) and Letšeng (life shortened, stripping deferred) show the reserve side; Lulo shows the value side — its 2024 valuation normalised modelled diamond values down 17% even as resource carats rose 9%.
Market timeline, 2021–2026
Dated market-context records: what prices did, why, and how producers responded.
All 60 records: estimates, changes and market context
Filter by section. Resources are stated inclusive or exclusive of reserves per each source; codes (JORC, NI 43-101, SAMREC), effective dates and product mixes differ between projects.
Project / record
Section
Date
Jurisdiction
Amounts & parameters
Cause / basis
Source
Caveats
Estimates follow different reporting codes and effective dates; some resources are inclusive of reserves, others exclusive. Diamond prices per carat (US$/ct) depend heavily on each deposit's rough product mix and size-frequency distribution, so price bases are not comparable across mines. Grades appear as carats per tonne (cpt) or carats per hundred tonnes (cpht); tonnages in Mt, contained diamonds in Mct. Where a source reports only an impairment or a simultaneous resource decline, no price causation is implied.
Method: 60 sourced rows assembled from 43 independent hosts (max 2 rows from any one URL) — 21 project resource/reserve estimates, 24 resource/reserve change records and 15 deduplicated market-context records, dated 2021–2026. Amounts are as stated by each source in Mt, Mct, cpt/cpht and US$/ct; categories reflect each source's stated cause. Long source passages were shortened for space; full detail is at the linked pages. A broad documented sample, not a census of all diamond deposits.