Hi!
Temporary solution until the author updates the mod settings:
In the mod folder, open the file "data-updates.lua", add the following text at the end, save the file.
if mods["space-age"] then
table.insert( data.raw[ "mining-drill" ][ "moho_extractor" ].resource_categories, "hard-solid" )
table.insert( data.raw[ "mining-drill" ][ "mantle_extractor" ].resource_categories, "hard-solid" )
end