In the Lumbay deposit, hydrothermal alteration associated with ore-grade mineralization is pervasive silicification, biotization and sericitization. The alteration pattern appears complicated in that, the usual zonal alteration patterns particularly of biotite and sericite are not clear cut because of widespread hydrothermal overprinting. Thus, even though the rocks have been thoroughly sericitzked, if biotized relicts constitute a significant volume of the rocks, these are classified into the biotite zone. Also, it is very frequent that the mineral assemblage in the biotite zone would include sericite.