As an alternative to the banana peels in the sump (hvy wt oil).......
Am I mistaken? - or aren't the bearings for the camshaft not slipper types - are they not journal bearings of aluminium as an integral part>
After the oil analysis that's already been suggested, I would start at the top and check camshaft end play firstly.
Then I would think about checking the condition of the bearing surfaces there....of course I could be wrong but this is another source of Aluminium.
There may be a rag on one bearing surface of the crankshaft that is tearing. these crankshafts are CI (cast iron) and it is feasible that if one were not conditioned properly (unlikely, I know) before final machining and surface grinding it may have distorted.
The days when a casting was thrown into a corner of the yard to mature are gone...everything is done in a rush and it is my experience with machining much CI that dimensional stability is attained over time and no amount of heat soak or whatever can circumvent the aging process of CI than time for stress relief.
One may've just slipped through the cracks and be tearing or be cracked......it may be that simple.
I would love to know if it is ferrous or not, first then I'd like to know what kind of Aluminium it is. That will tell you quite definitively where it comes from.
Depending on your findings - check for camshaft integrity (dye / X ray etc) true.....DTI when turned between centres or on V blocks....a bit of expertise need there.
If it is at the top end of the engine - not Good but not so bad either. It could be as simple as a lump of crud (coalesced carbon) scoring....who knows.
I agree with the chaps - I would stop driving until more info was gained.
Easy to say bit Don't stress - there WILL be a logical and likely relatively easy solution.
Good luck.