Geology and Ore Deposits of the Ma On Shan Mine, Hong Kong

Abstract

The Ma On Shan Mine is a typical contact-metasomatic iron ore deposit in the New Territories of Hong Kong. The ore deposits occur in the skarn zone along the contact plane between the Mesozoic formation and granite instrusive, and the cupola of the granite controls the ore deposition. Most of skarn minerals are rich in magnesium : diopside mainly occurrs in the outer zone of the skarn area, and amphibole in the inner zone. The former is formed in an earlier stage and the latter in a later stage. A large quantity of magnetite is found in the diopside skarn and small quantities of sulphide minerals in the amphibole skarn. High-grade magnetite ore deposits are found in two zones, and there are barren amphibole skarn and thick dolomitic limestone between the two zones.
It is concluded that the original rock of the deposits was dolomite, such ingredients as FeO, Fe₂O₃, AL₂O₃ and F were added in large quantity, and CaO, MgO and CO₂ were lost.