The Mamut porphyry copper deposit of upper Miocene age is located on the northern end of the island of Borneo. Copper mineralization is associated with an adamellite porphyry intrusion, and is localized in the intrusion as well as in the wall rocks which are composed of serpentinite and clastic sedimentary rocks. This paper deals with the serpentinite which has been altered hydrothermally by the mineralization.
The next four types of alteration for serpentinite are seen in the Mamut ore deposit: (1) weakly altered type, (2) chlorite type, (3) talc type and (4) tremolite type. The alteration process is considered to have proceeded in the following succession: (1) serpentinization of olivine and pyroxene, (2) formation of talc and chlorite from serpentine minerals, and (3) formation of tremolite from talc and chlorite. The alteration and mineralization process caused by the steps (1) and (2), which are considered to have been related to the intrusion of adamellite porphyry, is characterized by pervasive silicification and weak dissemination of chalcopyrite. Many fractures have been developed along the margin of the adamellite porphyry apophysis as the result of its cooling and shrinking. The process of the step (3) may be correlated with the introduction of mineralizing fluid, which has a high salinity and a high copper concentration, into the zone of well fractured adamellite porphyry and contiguous wall rocks. This alteration and mineralization process related to the step (3) is characterized by passive silicification and has completed the building up of the Mamut copper ore deposit.

抄録全体を表示

本地域は中新世のグリーンタフが広く分布する所で, その中に石見鉱床に代表されるいくつかの黒鉱型鉱床がある.鉱床周辺の岩石は黒鉱鉱化作用に関連した熱水変質を受けており,15本のボーリングコアのX線回折の結果,絹雲母一緑泥石帯は鉱床胚胎層準の久利層では黒鉱型鉱床周辺にのみ分布し,下部の川合,波多層では本地域の鉱床分布と同様東西の拡がりを示す.
絹雲母は鉱床隣接地域で,黒鉱型網状鉱体の層準では混合層鉱物となり,ほかでは純粋な絹雲母である.緑泥石は鉱床ではMg緑泥石で,その周辺ではFe-Mg緑泥石となり,鉱床で多い混合層鉱物は周辺ではほとんど認められないポリタイプは鉱床に隣接する所では鉱床と同じIIb型が認められ,ほかではIaのみである.
モンモリロン石一沸石帯は絹雲母-緑泥石帯の周辺に広く分布している. モンモリロン石のd(001)は久利層の下部または鉱床帯に近づくに従って減少する.これは鉱化作用の影響を受けて交換性イオン比Na/Cuが増加するためであり,Naモンモリロン石の生成は黒鉱鉱化に関連した熱水作用の末端現象と考えられる.
さらにコア試料中の脈鉱物に含まれる流体包有物の測定を行い,鉱化変質の著しい絹雲母―緑泥石帯の試料中の石英とい方解石脈から290°～160℃,カオリン化を受けた試料の方解石から155°～103℃の値が得られた.モンモリロン石-沸石帯の方解石脈からは184°～74℃またはそれ以下の値が得られている.
包有物液相の塩濃度は変質の種類に無関係に,充填温度が191°～165℃のものでは0.7～0.5wt%(NaC1相当)で,90℃以下のものではほぼ純水に近いということが解った.この事から天水起源の地下水による熱水溶液の稀釈もあると考えられる.

抄録全体を表示

The Maruyama orebody of the Tsumo mine belongs to the skarn type copper-zinc-tungsten deposit. Skarns are mainly classified into the following three types judging from their modes of occurrence and the mineral assemblages; banded skarn, massive skarn (vesuvianite-garnet-clinopyroxene skarn, wollastonite-garnetclinopyroxene skarn, and garnet-clinopyroxene skarn) and vein skarn (hedenbergite skarn). A copper-zinc mineralization took place in wollastonite-garnet-clinopyroxene skarn and garnet-clinopyroxene skarn, while a tungsten (scheelite) one is recognized not only in hedenbergite vein skarn, but also in the part of wollastonite-garnetclinopyroxene skarn.
Most of fluid inclusions in garnet, clinopyroxene and wollastonite are homogenized into liquid phase at about 300°-350°C. When the temperature correction is made considering salinity of the inclusion fluid and the formationlpressure on the basis of the sphalerite geobarometer, it is concluded that the formation temperature of the skarn minerals was about 400°-350°C.
Skarn minerals contain fluid inclusions, some of which are evidently primary in origin. Many of fluid inclusions contains solid phases, such as halite, sylvite, carbonate and metallic minerals. The variable volume ratio of the solid phases to the whole vacuole may suggest that the skarn minerals of the deposit were formed from saline solution of various concentrations. On the contrary, fluid inclusions in scheelite do not contain any solid phase. This implies that the mineral precipitated from a solution whose salinity was lower than 26 wt.% NaCl. Small grains of chalcopyrite are included in a sphalerite crystal. The fact that they array along a paticular plane may suggest that some of them is not the exsolution product, but minerals trapped during the growth of host mineral.
In general, fluid inclusions in skarn minerals have no liquid CO₂ phase at room temperatures. This turns out to be true for those in the Tsumo deposits. This fact agrees well with the conclusion derived from the solubility data of CO₂ for NaC1 solution and the calculated data for the stability field of the skarn minerals. However, the presence of gaseous inclusion, though the abundance is few, may suggest that two phase locally appeared during the skarn mineralization.

抄録全体を表示