| 1590 | Soga Riemon established copper smelting and coppersmithing in Kyoto. He developed a smelting technique called "Nanban-buki" to separate silver from copper and then worked on mine development. | |
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| 1691 | Operation of the Besshi Copper Mine started. | |
| 1905 | A refinery was established on Shisaka Island. | |
| 1927 | July | The management of the Sumitomo Joint-stock Company and the Besshi Mining Company was divided in order to establish Sumitomo Besshi Mining Co., Ltd. |
| 1937 | June | Sumitomo Besshi Mining Co., Ltd. and Sumitomo Coal Mining Co., Ltd. merged to establish Sumitomo Mining Co., Ltd. |
| 1939 | October | A plant for neutralization was completed in the refinery on Shisaka Island. This led to the complete solution of 50 years worth of smoke pollution at the end of the same year. (It was in September, 1893 that the Niihama smoke problem occurred.) |
| 1939 | November | Production of electrolytic nickel started. |
| 1946 | January | The company name was changed to Seika Kogyo (Mining) Co., Ltd. |
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| 1947 | July | Relocation of the headquarters to Tokyo started. (Relocation was completed in the spring of 1948.) |
| 1950 | March | The Metal Division of Seika Kogyo Co., Ltd. was divided to establish Besshi Mining Co., Ltd. |
| 1952 | June | The company name was changed to Sumitomo Metal Mining Co., Ltd., and at the same time, the original "igeta" emblem was revived. |
| 1954 | November | The company participated in the management of Taihei Metal Industry Co., Ltd. and expanded its business into nickel processing. |
| 1956 | September | The company established Hyuga Smelting Co., Ltd. and started production of ferronickel. |
| 1957 | March | The company established Asakawa Industrial Co., Ltd., the name of which was changed to Sumico Lubricant Co., Ltd. in 1962, and started production of a lubricant for which the raw material is molybdenum disulphide. |
| 1960 | April | The company established Tokyo Electronic Metal Co., Ltd. It then started to manufacture germanium dioxide, and expanded its business to electronic materials. |
| 1963 | April | The company established Siporex Manufacturing Co., Ltd to start production of ALC (Autoclaved Lightweight aerated Concrete). |
| 1963 | August | The company established Sumiko Consultants Co., Ltd. (currently Sumiko Resources Exploration & Development Co., Ltd.) and expanded its business to consultancy on geology, mineral deposit investigation, etc., at home and abroad. |
| 1964 | July | The company established Sumiko I.S.P. Co., Ltd. |
| 1965 | August | Central Research Laboratories (currently Ichikawa Research Laboratories) was completed. |
| 1966 | April | The company absorbed Tokyo Electronic Metal Co., Ltd., and set up the Electronic Metal Division (currently Materials Div.). The Harima Smelter (currently Harima Refinery) of Sumiko I.S.P. Co., Ltd. was completed and production of zinc and lead started. |
| 1967 | September | The Ome Plant of the Electronic Metal Division was completed. |
| 1969 | March | The company's electlytic copper was registered on the London Metal Exchange (LME). |
| 1970 | April | The company established Nippon Ketjen Co., Ltd. and expanded its business to the field of desulphurization catalyst. |
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| 1971 | February | The Toyo Smelter was completed. |
| 1973 | March | The Besshi Copper Mine was closed. |
| 1973 | May | The Kounomai Mine was closed. |
| 1974 | June | An electronics materials plant was completed in the Kunitomi District Div (currently Sumiko Kunitomi Denshi Co., Ltd.)., and production of germanium started. |
| 1977 | January | Sumitomo Metal Mining Singapore Pte. Ltd. was established. Production of lead frames started in Singapore. |
| 1977 | February | Niihama Research Laboratories was established. |
| 1979 | June | The Sazare Mine was closed. |
| 1980 | October | The company absorbed Sumiko I.S.P. Co., Ltd. to establish the Harima Smelter (currently Harima Refinery). |
| 1981 | September | High-grade gold ore veins were discovered in the Hishikari Mine in Kagoshima Pref. by the Metal Mining Agency of Japan. |
| 1981 | October | Ohkuchi Electronics Co., Ltd. was established. |
| 1982 | April | The company' new headquarters building (Shimbashi Sumitomo Building) was completed. The result of minerals prospecting at the Hishikari Mine was announced (it was expected that 120 tons of gold existed). |
| 1983 | April | The Hishikari Mine was opened. |
| 1985 | July | The ore veins of the Hishikari Mine were reached and removal of ores started. |
| 1986 | February | The company and Sumitomo Corporation jointly invested in the Morenci Copper Mine (Arizona), owned by Phelps Dodge Corporation (currently Freeport McMoRan Inc.). |
| 1987 | February | The company reformed its organization. The company introduced a divisional system. |
| 1988 | May | The company took equity participation in P.T. International Nickel Indonesia (currently PT Vale Indonesia Tbk) in Indonesia. |
| 1988 | October | Niihama Electronics Co., Ltd. was established. |
| 1989 | April | M-SMM Electronics SDN. BHD. was established. Production of lead frames started in Malaysia. |
| 1989 | October | The company absorbed Siporex Manufacturing Co., Ltd. |
| 1990 | April | The company integrated three copper and brass companies to establish Sumitomo Metal Mining Brass & Copper Co., Ltd. |
| 1990 | July | The company took equity participation in Ballande (currently Figesbal in New Caledonia). |
| 1990 | November | A ceremony of the 300th anniversary of the Besshi Mine opening was held. |
| 1992 | January | The company participated in the Candelaria Copper Mine development project by Phelps Dodge Corporation. |
| 1993 | April | The Niihama Nickel Refinery completely changed its metal refining process to the MCLE (Matte Chlorine Leach Electrowinning) method. |
| 1993 | June | The company participated in the Northparkes Copper and Gold Mine development project. |
| 1994 | November | Sumiko Electronics Taiwan Co., Ltd. was established. Production of lead frames started in Taiwan. |
| 1995 | September | The company took equity participation in Jinlong Copper Co., Ltd. in China. |
| 1995 | October | Shanghai Sumiko Electronic Paste Co., Ltd. (SEP) was established. Production of paste started in China. |
| 1996 | January | Sumiko Leadframe (Thailand) Co., Ltd. was established. Production of lead frames started in Thailand. |
| 1997 | June | The accumulated amount of gold yielded in the Hishikari Mine (83 tons) became the largest in Japan. |
| 1998 | January | The company took equity participation in the Batu Hijau Copper and Gold Mine development project in Indonesia. |
| 1998 | May | The company acquired shares in Teck Corporation (currently Teck Resources Limited, Canada). |
| 1998 | October | It was confirmed that the amount of gold in the Liese Deposit in Stoneboy, Alaska was 162 tons. |
| 1998 | November | Sumiko Leadframe Chengdu Co., Ltd. was established. A lead frame business in China was also started. |
| 1999 | September | A critical accident occurred in the Tokai Division of JCO Co., Ltd. |
| 1999 | September | As a spin-off of the Building Materials Division, Sumitomo Metal Mining Siporex Co., Ltd. was established. |
| 2001 | July | The project for developing low-grade nickel oxide ore from the Riotuba Mine (the Coral Bay Nickel Project) in the Philippines started. |
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| 2002 | July | A business alliance was formed with Mitsui Mining & Smelting Co., Ltd., concerning zinc refining business, to establish a joint venture, MS Zinc Co., Ltd. |
| 2003 | February | Concerning sulphuric business, a business alliance was formed with Dowa Holdings Co., Ltd. to establish a joint venture, Acids Co., Ltd. |
| 2003 | March | Sumiko Electronics Suzhou Co., Ltd. was established. This company is our second lead frame production base in China. |
| 2004 | October | A basic agreement was made to take equity participation in the Cerro Verde Copper Mine development project in Peru. A basic agreement was made to take equity participation in the project for developing Goro Nickel Mine in New Caledonia. |
| 2005 | April | A joint venture, GRANOPT Co., Ltd., was established between our company and MItsubishi Gas Chemical Company Inc. for rare-earth iron garnet (RIG) business. Commercial production by the Coral Bay Nickel project in the philippines started. |
| 2005 | December | We took equity participation in the Ojos del Salade Copper Mine project in Chile. |
| 2006 | February | Production at the Pogo Gold Mine (Alaska, USA) started. |
| 2006 | November | Cerro Verde copper mine commenced production of copper concentrate. |
| 2009 | July | The company and Sumitomo Corporation acquired all rights from Teck Resources Limited’s Pogo gold mine |
| 2009 | August | The company took equity participation in Nickel Asia Corporation (the Philippines). |
| 2009 | September | The company decided to implement the Taganito Project (the Philippines). |
| 2010 | July | Concerning the consolidation of the copper and copper alloy fabricated businesses of Mitsui Mining & Smelting Co., Ltd. and Sumitomo Metal Mining Co., Ltd. |
| 2010 | October | Split up of the Shisaka Factory, which operated around coarse zinc oxidized materials, establishing Shisaka Mine Co., Ltd. |
| 2011 | September | The company participated in the Sierra Gorda Copper Mine development project of Quadra FNX Mining Ltd. (currently KGHM International Ltd.) in Chile. |
| 2012 | July | Sumitomo Metal Mining Management (Shanghai) Co., Ltd. was established to perform sales and management tasks in China. |
| 2013 | September | Commercial production started at Taganito HPAL Nickel Corporation in the Philippines. |
| 2015 | July | Production at Sierra Gorda Copper Mine (Chile) started. |
| 2016 | May | The company acquired additional interest in the Morenci Copper Mine (Arizona, USA). |