TL;DR: if no animals are harmed and no animal products are used, then yes, it's considered vegan.
A product of "purely mineral origin" will be considered vegan if no animals are exploited in the process of producing it, since, as vegans we avoid using animals and animal products for our own ends wherever possible.
As far as I know, the synthesis of L-Ascorbic acid doesn't involve the use of animal products; vitamin C supplements I have seen are labelled as vegan (with the exception of gelatin capsules)
However, the article you link to is interesting:
Following the isolation of crystalline "hexuronic acid" from the adrenal cortex of the ox and from orange juice in 1928 [...] efforts were begun to synthesize this novel vitamin...
This highlights the history of animal experimentation behind vitamin supplements, and, to me, the fact that veganism is in a sense aspirational, since in the last analysis it's impossible to avoid some degree of responsibility and complicity in causing suffering to other animals.