670 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



mineral was obviously the same which Koto had called ilvaite 2 and 

 Higgins had 3 had described as a new species under the name "coll- 

 branite," its investigation was deemed necessary. Analysis has 

 shown the material in each of the several specimens to be ludwigite. 4 



Occurrence. — The occurrence of the ludwigite has been well de- 

 scribed by both Koto and Higgins in the papers cited, although both 

 authors erred in their identification of the mineral. The deposit, 

 which is mined for gold and copper, occurs as irregular masses of 

 lime-silicate minerals at the contact of granite with limestone. The 

 lime-silicate hornfels in irregularly impregnated with ludwigite, 

 bornite, and chalcopyrite, mingled with some chalcopyrite and a 

 little galena and magnetite. The less metamorphosed limestone 

 contains a little diopside and a uniaxial variety of serpentine, while 

 the more intensely altered phase consists of about equal volumes 

 of calcite and contact-metamorphic minerals. This is impregnated 

 with auriferous sulphides in addition to the ludwigite and diopside, 

 the ludwigite-bearing limestone being the ore body of the Hoi Gol 

 Mine. Local bodies of diopside rock and of garnetite occur in the 

 ore-bearing zone. Muscovite is mentioned by Koto as occurring 

 in the ore while, according to Higgins, phlogopite is very abundant, 

 masses of pure phlogopite many tons in weight being encountered 

 at times. It is evident from the descriptions that the ludwigite is 

 common and present in large amount in the mine. 



Description of associated minerals. — The specimens examined by 

 the writer are all very similar in appearance, all consisting of sheaves 

 and rosettes of shining black needles of ludwigite embedded in a 

 white or grayish-white granular groundmass. The aggregates of 

 the ludwigite may reach a centimeter in maximum diameter and 

 are rather uniformly disseminated in their matrix. When examined 

 under the microscope in thin section this matrix is seen to consist 

 in the main of calcite in large twinned grains with disseminated 

 irregular grains of colorless diopside. All of the grains of calcite 

 when at the position of extinction between crossed nicols, show 

 numerous minute flakes of a mineral resembling talc as though some 

 magnesia in the original limestone had separated out in this form 

 during metamorphism. Small masses and grains of bornite are 

 visible in one specimen. None of these are included in the thin 

 sections studied and no other ore minerals were seen. The lud- 

 wigite is included in the calcite and does not encroach upon the 



* Koto, B., Geology and Ore Deposits of the Hol-Gol Gold Mine, Journal College Science, Imperial Univ- 

 Tokyo, vol. 27, art. 12, 1910. 



3 Higgins, D. F., Geology and Ore Deposits of the Collbran Contact, Suan Mining Concession, Korea. 

 Economic Geology, vol. 13, p. 19, 1918. 



* The analysis has already been published with a short note identifying collbranite with ludwigite. Shan- 

 non, E. V., Amer. Mineral, vol. 6, p. 87, 1921. 



