There may be limited alluvial Mn ore which the artisan miners dig up, but I think there are billions of tonnes of Mn ore in West Timor (East Nusa Tenggara) or Timor Barat.
There are at least 13 major volcanic plugs with the biggest being approx. 3000m x 1400m x 100m high (and that's only above ground).
The main problem is getting the farmers onside.