Relationship between the Percentages of Cold-Extractable Copper to Total Copper in Stream Sediments and Copper Deposits

Abstract

The contents of total copper (T-Cu) and cold-extractable copper (Cx-Cu) and the percentages of Cx-Cu to T-Cu in stream sediments were examined for three types of copper deposits, net-work, vein, and porphyry copper type deposits. The study indicates that geochemical exploration only by Cx-Cu in stream sediments is not adequate for locating orebodies, because hydromorphic trains are found at greater distances from mineralized areas. The anomalies delineated by T-Cu in stream sediments are composed of clastic and hydro-morphic trains. In some places, the latter is so storng, especially in humid tropic areas, that the anomalous areas delineated by T-Cu do not always related to the mineralized areas. In such cases, only clastic anomalies can disclose mineralized areas.
Variation of the. percentages of Cx-Cu to T-Cu may be a useful indicator for mineralization and it may be considered that the decreasing point of the percentages shows the entrance of a clastic anomaly which may be located above mineralized bodies. If values of Cx-Cu and T-Cu at each sampling site are nearly same and only hydromorphic anomalies are obtained, we may consider that blind copper ore deposits are expected near the hydromorphic anomalies which are caused by mixing drainage and ground water running through blind ore deposits.
(1) Kamanai deposit (Miyagi Pref., northern Japan)
A net-work deposit occurs in Miocene propylyte covered by post-mineralization dacite tuffs of Pliocene. An anomalous level of T-Cu appears in the area of the mineralization, but the values of Cx-Cu do not show much difference between the mineralized area and the non-mineralized area in the downstream. The percentages of Cx-Cu to T-Cu decrease sharply in the mineralized area, showing the hydromorphic precipitation in the downstream.
(2) Kunimiyama deposit (Miyagi Pref., northern Japan)
The deposit consists of many small copper veins in Miocence andistic tuff. The level of T-Cu does not show any difference between the mineralized and non-mineralized areas, but that of Cx-Cu decreases sharply in the mineralized area, showing high precipitation of hydromorphic copper in the downstream. This high precipitation of Cx-Cu seems to be caused by abundant supply of leached copper from old dumps. Such an abundant supply of leached copper from copper deposits would be common in tropical humid terrains.
(3) Mamut deposit (Sabah, Malaysia)
This deposit is located on the eastern flanks of Mt. Kinabalu (4, 101 m), the highest mountain in Borneo. The topography is very rough with heavy forest cover. The annual pre-cipitation is about 3, 500 mm. The deposit is of porphyry copper type and consists of dissemination of pyrite, chalcopyrite, chalcocite, and a small amount of molybdenite in association with storong siliciacation of diorite porphyrite stock which intruded into Tertiary sedimentary rocks and ultrabasic rocks. The anomalous levels of T-Cu and Cx-Cu appear in the downstream of the ore deposit. But the percentages of Cx-Cu to T-Cu clearly decrease in the area of the ore deposit, showing high precipitation of leached copper from the deposit.