Dust flux, Vostok ice core

Dust flux, Vostok ice core
Two dimensional phase space reconstruction of dust flux from the Vostok core over the period 186-4 ka using the time derivative method. Dust flux on the x-axis, rate of change is on the y-axis. From Gipp (2001).

Sunday, April 21, 2013

Size distribution of global deposits redux

Same idea as last time, but working from an updated database of 439 gold deposits of one million ounces or more.

Size distribution of global gold deposits on log-log scale. Data from NRH.

The chart is a graph of the number of gold deposits larger than a certain size, with both axes plotted on a logarithmic scale. The point at the upper right tells us that there is one deposit (in this case, the Pebble Deposit) larger than 88.1 M oz (which is the size of the number 2 deposit, Grasberg). The point at the far left tells us there are 438 deposits larger than 1 M oz.

In an ideal scale-invariant system, the points would line up on a straight line. We don't expect to see this completely here for two reasons: 1) not all gold deposits have been discovered; and 2) we don't really have a consistent definition for a deposit. Some deposits are so large that in settings where concessions would be smaller, they might count as several separate deposits. One might argue that all of the gold deposited in a geological province during one ore-forming event should count as a single deposit. If so, then the number of deposits on our chart above would be much smaller, and their average size would potentially be larger.

There is a noticeable break in the slope at about the 2,000,000 ounce size--the number of smaller deposits falls off more rapidly than would be expected given the number of deposits greater than 2 M oz. This may be a reflection of a bias towards larger deposits. In financing discussions over the past few years it has been made clear to me that there is not a lot of interest in deposits smaller than 2 M oz.

We are grateful to Natural Resource Holdings for taking the time and effort to put this list together.
The line in the above plot would suggest that there are still at least 500 deposits of 1 million oz or more still to be discovered. This would suggest that we have discovered only about half of the total gold deposits > 1 M oz in size that there are to be discovered. I would contend that we have a lot more to discover.

As above, with last year's reported distribution in blue.

In the last year, NRH added 200 deposits to their list. These were not all newly discovered or bumped up to this level--clearly, the majority of these additions had been missed the first time. It is reasonable to assume that there are still some deposits in this category that have been missed in the 2012 report, so that the 2013 report will have more deposits, but probably not 200 more. What I don't think will change significantly is the above estimate--that our present discoveries are less than half of what gold remains to be discovered.

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