Hans (or Johannes) Merensky, mining engineer and prospector, was the son of the missionary Alexander Merensky* and his wife Marie Liers. The family moved from South Africa to Berlin, Germany, in 1882 when Hans was eleven years old. After completing his schooling and a year's military service he spent a year in the coal mines of Silesia before entering the Breslau Technische Hochschule (a technical university). After further practical training as a mine overseer in the Saar he continued his studies at the Technische Hochschule in Berlin for another year and a half, qualifying, with distinction, as a "Bergreferendar" (first-stage mining engineer). Then followed a period of nine years of intermittent study and practical experience after which he qualified as "Bergassessor", or mining engineer, with geology as his major subject. He was subsequently employed in the Prussian Department of Mines.
In about 1904 Merensky came to South Africa on study leave to report on mining activities in the country. However, some time after his arrival he resigned from his post and started a successful private practice as a consulting geologist and mining engineer in Johannesburg. His main activity was to identify, analyse and evaluate mineral samples. During his first year in the country he published a note on new occurrences of tin in the Transvaal (in several German Journals), and a "Technical report on the Premier Diamond Mine" in South African Mines. In 1905 Friedlaender & Co. sent him to Madagascar to investigate a sensational gold rush. After a thorough investigation, he found that the high gold values reported by the Lecomte-Madagascar Gold Concession had been obtained by "salting" and exposed the whole venture as a swindle. Among others he studied the diamond finds near Luderitz, on the coast of German South West Africa (now Namibia), and reported his observations in the Transactions of the Geological Society of South Africa under the title "The diamond deposits of Luderitzland, German South-West Africa" (1909). Contrary to the opinion of most other geologists he thought that the diamonds came from a kimberlite pipe in the sea, rather than from inland. Other papers by him in the same journal included "The origin of the river diamonds within the area of the Vaal" (1908), "The gold deposits of the Murchison Range in the north-east Transvaal" (1908) and "The rocks belonging to the area of the Bushveld Granite Complex in which tin may be expected" (1908). More papers by him appeared in German journals around this time. By 1906 he was a member of both the Geological Society of South Africa and of the South African Association for the Advancement of Science.
Though Merensky's practice was a financial success he speculated heavily on the stock market, with the result that he was declared insolvent in 1913. During World War I (1914-1918) he was interred in the concentration camp at Fort Napier, near Pietermaritzburg, because he was an officer in the German Army Reserve. After his release in July 1919 he had to recuperate from serious illness and then found it difficult to obtain work during the post-war depression.
In June 1924 Merensky received a small amount of alluvial platinum that had been found by A.F. Lombaard on his farm Maandagshoek in the Lydenburg district. After a brief visit to the farm he and some German businessmen founded the Lydenburg Platinum Syndicate and he commenced an intensive search for the mother lode in August. Within a few days he found the first platinum bearing dunite pipe on the farm Mooihoek. During the first half of September, with the help of several other prospectors, he discovered the first portion of the now famous Merensky Reef, a mineralised pyroxenite layer in the norite of the Bushveld Igneous Complex. They traced the reef over a distance of many kilometers and Merensky gained control of the mining rights over a large area for his syndicate. Eventually the reef was shown to extend for some 300 km and to represent the largest known platinum deposit in the world. Merensky first described the discovery in an unpublished report for the Lydenburg Platinum Syndicate, "The various platinum occurrences on the farm Maandagshoek No. 148", dated 31 December 1924. He published his finds in "Report of Potgietersrust Platinum" and "How we discovered platinum" in the Mining and Industrial Magazine of Southern Africa (1925), and in several other articles in both local and German journals. He made just enough money to pay off his earlier debts and take a holiday in Germany.
While still in Germany he heard that diamonds had been discovered on the Namaqualand coast and hurried back to South Africa to investigate. Based on his earlier observations of the diamond deposits south of Luderitz he speculated that the diamonds were associated with an oyster line formed by shells of the extinct species Ostrea prismatica. Arriving in Namaqualand in December 1926 he managed to obtain 23 claims and further open ground, including a large section of the oyster line, in the name of the Hans Merensky Association, in which he had a holding of 50%. His prospectors found numerous diamonds of large size and high quality along this line. To prevent a collapse of the diamond market Merensky persuaded the government of the Union of South Africa to close the entire area to further prospecting. He sold his interests to the Oppenheimer-Barnato group for a large sum and described his views and experiences in "How I found the richest diamond fields in the world" (Mining and Industrial Magazine of Southern Africa, 1927) and "The discovery of the Namaqualand diamonds" (South African Mining and Engineering Journal, 1928). At this time he also wrote a paper on "Artesian water in Namaqualand" (Ibid, 1928.
Following his success Merensky bought the estate Westfalia near Duiwelskloof in the Transvaal, where he experimented with various crops, had the Merensky dam built, developed methods to combat soil erosion, and conducted various other agricultural experiments. The estate became a model of conservation. He later bought several other farms in the Transvaal and also bought and developed several estates in Germany. By this time he was convinced that the Witwatersrand gold-bearing deposits should extend into the Free State and in 1936 provided financial assistance to a syndicate drilling for gold near Odendaalsrus. Rocks of the Witwatersrand Supergroup were found, but he sold his interest in the venture the next year. In 1937 he bought the farm Jagdlust, south-east of Polokwane, on which he discovered and developed an extremely rich deposit of chrome ore. That same year he explored an extensive deposit of high quality vermiculite at Loole Kop, near Phalaborwa, which was subsequently mined by his Transvaal Ore Company.
Merensky financed a chair of forestry and the erection of the physics building at the University of Stellenbosch, as well as the Merensky Library at the University of Pretoria. At the outbreak of World War II in 1939 he retired and settled on Westfalia. However, after the war, at the age of 75, he set up camp at Loole Kop, near Phalaborwa, and during the next three years supervised the prospecting and drilling which exposed its huge phosphate deposits. The state bought the claims and established the Phosphate Development Corporation (Foskor) to mine the deposit. Merensky then finally retired to his farm, in failing health and increasing deafness. He set up the Hans Merensky Trust, later converted into the Merensky Foundation, with the aim of completing his current projects and thereafter helping to develop South Africa's natural resources and preserving its soil, water, flora and fauna.
Merensky was the greatest prospector and discoverer of mineral deposits in South Africa's history and was credited with an uncanny sense for finding minerals by geologists as well as the general public. Although the initial mineral finds were almost always made by others, his unique contribution was based on his geological knowledge, exceptional powers of observation, and persistent thoroughness. In 1926 the Technische Hochschule of Berlin awarded him an honorary doctoral degree in engineering. In later years honorary doctorates were conferred upon him also by the Universities of Stellenbosch and Pretoria. He was awarded the David Draper Medal of the Geological Society of South Africa in 1948, and the Leibnitz Medal of the Prussian Academy of Sciences in 1938. A rather introverted man, he never married and associated mainly with German speaking persons in South Africa.