Interesting....
Some rough numbers/analysis that may help others interpret what we are seeing:
Ore mined in 2020 was circa 350,000 bcm (see table below), which equates to about 945kt at 2.7t/bcm
We processed almost 1.1Mt (wmt) of ore, including the stockpiled contaminated ore.
217kt (circa 20%) of the plant feed came from contaminated stockpiles (see Dec qtry report).
The total stockpiled ore remains at about 3Mt at the end of 2020 (same as at the beginning of 2020) (see table below).
So, what we consumed from the stockpiled ore in 2020, we effectively replaced with newly mined ore.
Above numbers don't all add perfectly up due to adjustments required for dmt vs wmt, SG assumptions, ore-sorting mass yield, etc.
However, plenty of ore remaining in stockpiles. No big deal.
We sold about 150kt SC @ 5.8% Li20 in 2020.
Product inventory reduced by about 48kt for the year (65kt at start to 17kt at end).
So, roughly, we "consumed" about 102kt @ 5.8% from our "reserves" (i.e. from in-situ and stockpiled ore).
That is about 5,900t Li20.
Factoring in plant recovery of 54%, that is about 11,000t Li20 fed to the plant.
So, we "consumed" a quantity of ore containing about 11,000t Li20 for the year.
At an avg grade of 1.11%, that equates to about 991kt of ore.
(actually a bit more than this due to the mining recovery factor)
Today's announcement states:
"In 2020, Mt Cattlin Ore Reserve depleted by 0.25Mt"
250kt.
But we consumed about 1Mt of ore, suggesting that all else being equal, we should have depleted our ore reserves by about 1Mt.
Great!?
So, the difference in remaining ore reserves, expected vs actual, (very significant btw) is due to adjustments for factors including dilution and mining recovery, as noted in the report.
Even at a high-level glance (i.e. ignoring most of the working above), we mined almost 1Mt of ore in 2020, yet our in-situ reserves (proven and probable) have "only" decreased from around 5.3Mt to around 5.0Mt.
Great: more ore remaining than anticipated.
However, not-so-great: grade adjustments reduce the remaining contained-metal..
Contained-metal reserve estimates have reduced from about 107kt Li20 to about 90kt Li20. A reduction of about 17kt.
But, we consumed about 1Mt of ore at circa 1.11% Li20, equating to about 11kt Li20.
So, the bottom line is that amongst various assumptions regarding grade, dilution, recovery etc, we now think we have very slightly less Li20 reserves than we anticipated a year ago: earlier estimates suggested we should have around 96kt Li20 remaining @ 31 Dec 2020; current estimates suggest around 90kt Li20 remaining.
No big deal imo, especially considering the sensitivity of remaining Li20 reserves to modifying factors such as recovery and dilution effects.
Perspective!
Not double-checked, DYOR!!
