Sure it can suggest causation. It is not proof, but can justify scientific investigation.
I've plotted the prices of a dozen geological commodities from 1900 to 2008. (Gold, silver, copper, aluminum, steel, tin, lead, gypsum, salt(sodium chloride), potash,...
On a logarithmic charts they trended linearly with roughly the same slope.
Plotted linearly they trended to nearly identical exponential curves.
A quick glance the OP's chart suggests the same tendency.
What it suggests to me is that banker's money is broken and it leaks value. Nine percent per year on average for the last 100 years.
Free includes debt-free!
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