41. Additionally, 9 stamp mills were in operation. 42. In 1915, a stamp mill was built. 43. By 1882, a 5-stamp mill was operating. 44. Stamp mills were invented in Europe in the 1600s to crush ore to extract minerals, especially gold.45. Working 150 men, the two rapidly opened up the Bonanza King and put up a 20-stamp mill . 46. After completing his studies in 1840, he immediately became a stamp mill inspector in the civil service. 47. The Bald pulverizer had been started previously and run a short time, but was not a stamp mill . 48. After 1850 the small and scattered stamp mills and ore washeries were replaced by central ore dressing plants. 49. After the installation of the twenty stamp mill , water supplies were insufficient for efficient operation of the mill. 50. Stamp mills were used by Islamic Spain and North Africa in the west to Central Asia in the east.
