Sentence:  ... the loss of gold was still as high as 25 percent. This is one of the reasons why most early <WSD>quartzing</WSD> operations soon failed. There were thirty-nine mills in 1854 .... By 1858, there were 279 <WSD>quartzing</WSD> mills operating. Although <WSD>quartzing</WSD> was practiced in each of the Mother Lode counties, ... 
Meaning of the word marked with <WSD> tags:  The extraction of quartz from the earth, and moreover the subsequent extraction of gold from quartz.