Mineral reserves

Reserve. That portion of an identified resource from
which a usable mineral or energy commodity can be
economically and legally extracted at the time of
determination. The term “ore” applies to reserves
of some kinds of mineral commodities, generally
metallic, but for want of another term it is sometimes applied to nonmetallic commodities.

Note the “economically” and “legally” there. A Mineral reserve is where you have demonstrated – proven to, say, JORC terms – that you can extract at a profit. Legally means that you’ve got the licences to do so.

It’s the amount in known to be profitable and licenced to open mines. Nothing – at all, in no way related in any manner – to the amount that is out there that could be extracted.

Or:

Reserves may be considered a
working inventory of mining companies’ supplies of an
economically extractable mineral commodity.

And:

Some countries have specific definitions for reserves
data, and reserves for each country are assessed
separately, based on reported data and definitions. An
attempt is made to make reserves consistent among
countries for a mineral commodity and its byproducts.
For example, the Australasian Joint Ore Reserves
Committee (JORC) established the Australasian Code
for Reporting of Exploration Results, Mineral Resources
and Ore Reserves (the JORC Code) that sets out
minimum standards, recommendations, and guidelines
for public reporting in Australasia of exploration results,
mineral resources, and ore reserves. Companies listed
on the Australian Securities Exchange and the New
Zealand Stock Exchange are required to report publicly
on ore reserves and mineral resources under their
control, using the JORC Code.
Data reported for individual deposits by mining
companies are compiled in Geoscience Australia’s
national mineral resources database and used in the
preparation of the annual national assessments of
Australia’s mineral resources. Because of its specific
use in the JORC Code, the term “reserves” is not used
in the national inventory, where the highest category is
“Economic Demonstrated Resources” (EDR). In
essence, EDR combines the JORC Code categories
proved reserves and probable reserves, plus measured
resources and indicated resources. This is considered
to provide a reasonable and objective estimate of what
is likely to be available for mining in the long term.
Accessible Economic Demonstrated Resources
represent the resources within the EDR category that
are accessible for mining. Reserves for Australia in
Mineral Commodity Summaries 2020 are Accessible
EDR. For more information, see table 3. Australia’s
Identified Mineral Resources as of December 2017 can
be found at https://d28rz98at9flks.cloudfront.net/124309
/124309_AIMR.pdf.

Not precisely and wholly and exactly but pretty much. Mineral reserves – in those global estimates that all the environmentalists like to look at – are compiled from the data companies report to stock exchanges of the minerals they’ve got in their particular mines. That is, it’s the stock exchanges that determine what mineral reserves are. There is no geologic input into this. There is no global survey. It’s a purely financial totting up.

And therefore, of course, entirely useless as an estimation of how much there is out there that we might be able to use.