Hitting the Mother Lode

Mother Lode of CA – 1900

If you’ve ever heard someone exclaim, “I’ve hit the Mother Lode!” you know that person has probably discovered some great prize or fortune. But did you ever wonder where this odd expression originated?

In honor of Mother’s Day, we’ve decided to explore this unique, and as it turns out, history-rich phrase. The term “Mother Lode” first became popular during the California Gold Rush but actually refers to a region of California. The California State Mining Bureau published a bulletin written in 1900 by A.S. Cooper, a state mineralogist, that described the Mother Lode Region of California.

The Mother Lode, also known as the California Gold Belt, actually has several divisions as opposed to one giant section of gold-bearing veins. According to Cooper, “Throughout the entire length of the great synclinal trough of the Gold Belt are found the gold-bearing veins which constitute the so-called Mother Lode. It seems unfortunate that the name was ever given to this portion of the Gold Belt as it conveys to the minds of those unfamiliar with the geological structure and veins of the region, an impression of a continuous, unbroken vein. That such a condition does not exist is well known to those familiar with these mines.”

Later, in 1934, Clarence A. Logan of the State of California Division of Mines, also published a bulletin on the Mother Lode Gold Belt of California. He described the discovery of the area as a result of a “search in the 1850s and 60s to find the so-called ‘mother’ vein or lode as the source from which the gold in the gravels had been derived by Nature’s process of erosion.” One of the two most productive districts extended through the counties of El Dorado, Amador, Calaveras, Tuolumne and Mariposa, and became known as the Mother Lode Gold Belt. George Nordenholt, the Director of State Department of Natural Resources at the time, described this area as “not a single vein or lode, but a zone or belt up to a mile wide for a distance of 120 miles from northwest to southeast, within which are separate and discontinuous veins of gold-bear quartz.”

Logan also described the distinguishing characteristics of the Mother Lode: a uniform strike, north to northwest; uniform dip east or northeast at a rather steep angle, and association with certain rocks of slaty or schistose character, particularly Mariposa clay slate, altered andesites, and altered peridotite and serpentine all of which have been subjected to great compressive stresses or hydrothermal alteration along the distinct overthrust fault zone which has given access to mineralizing solutions from deep-seated sources (probably granitic batholiths). He went on to note that the “term lode is particularly applicable to this vein system as most of the mines show two or three practically parallel veins, often with subordinate spurs, all occurring within generally definite walls, but with no vein traceable as a rule for any great length of the strike.” (We still use the term “Lode Gold Deposits” today to refer to rich gold veins.)

This archived Bulletin is an interesting read into history, discussing the courage and imagination of the pioneer miners as well as the setbacks they faced and the work they did before modern transportation, water or electric facilities were available. It was certainly nothing like the work accomplished by mining operations today that have technologies including x-ray fluorescence (XRF) analyzers, laboratory information management systems, bulk weighing and monitoring systems, and mineral analyzers and sampling systems at their fingertips.

What do you think is the most important modern-day mining innovation?