ティサパ鉱山の現況と開発後の知見
2000 年 50 巻 1 号 p. 1-10
詳細
2000 年 50 巻 1 号 p. 1-10
The Tizapa mine located in Mexico State, Mexico, started production in 1994 and is now producing 40, 000t/month of crude ore by the Minera Tizapa S.A de C.V., a joint venture among Penoles, Dowa Mining Co., Ltd. and Sumitomo Corporation.
The Tizapa deposit is a strata-bound volcanogenic massive sulfide (VMS) type deposit and its characteristics are very similar to that of Kuroko deposits in Japan. Though the present shape of the ore deposit looks composed of several layers of ore bodies because of many folding and thrust faults, the ore deposit is thought to be originally a single lenticular ore body emplaced at the contact of footwall sericite-chlorite schist and hanging wall graphite schist.
The footwall sericite-chlorite schist can be distinguished in appearance, one greenish colored "chlorite schist" and whitish "sericite schist". Immobile element study, however, shows that the protolith of "chlorite schist" and "sericite schist" are both classified into andesitic to dacitic rock and doesn't show significant geocherrlical difference.
The alteration halo of the footwall sericite-chlorite with Alteration Index more than 70 is observed around the ore deposit. This fact suggests the original alteration zone in the footwall volcanic rocks of the Tizapa VMS deposit is preserved even after the metamorphism.
Low resistivity zone detected by transient electromagnetic (TEM) method has a good correlation with the location of the ore deposit. It is understood that the hanging wall graphite schist is the cause of the low resistivity and the TEM method is effective to interpret the structure and to predict the depth of ore horizon at the Tizapa area.
The Tizapa deposit is older in geological age (before early Cretaceous) than Kuroko deposits in Japan (middle Miocene), but both have very similar characteristics and the same exploration method can be applied. It is proposed that most effective exploration method in the Tizapa area is to clarify the stratigraphy and to pursue the ore horizon with the guidance of the alteration halo in the footwall unit.
