Collection: Books and Periodicals

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Title: The Tertiary Gravels of the Sierra Nevada of California by Waldemar Lindgren (1911) Collection Type: Books and Periodicals Source(s): Google Books # of Pages: 301 Download PDF: User Login Required Download OCR Text: User Login Required

Date Scanned: 2024-07-14 06:26:22 Item Sourced From: PDF First Created: 2025-03-17 05:53:20 Last Updated: 2025-03-17 05:53:20

Original Held At: Searls Historical Library Location: 161 Nevada City Hwy, Nevada City, CA 95959

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66 TERTIARY GRAVELS OF THE SIERRA NEVADA OF CALIFORNIA. the great Mother Lode are either eroded or so heavily covered that they can not be mined. This great source of enrichment being absent, the general grade of the gravels in these counties is lower than in those farther north. In Tuolumne County, just previous to the Table Mountain flow, a drainage channel was established for a short time across the Mother Lode and this watercourse, covered by a basaltic flow of great resistance, has escaped subsequent erosion. The gravels deposited in it have been mined underneath the Table Mountain west of the Mother Lode. They were rich in places, but the channel existed for too short a time to become heavily enriched. Smaller patches of gravel preserved in the same position west of the Mother Lode, as near Chinese Camp, have proved very rich. South of Tuolumne County few Tertiary gravels have been preserved from erosion. The geographic relations sketched above in merest outline prove conclusively the dependence of the gravels for their enrichment on the distribution of the primary vein deposits, and it may be safely asserted that the gold in the channels is almost exclusively derived from such deposits. DISTRIBUTION OF THE GOLD IN THE GRAVELS. It has become almost an axiom among miners that the gold is concentrated on the bedrock and all efforts in placer mining are generally directed toward finding the bedrock in order to pursue mining operations there. It is well known to all drift miners, however, that the gold is not equally distributed on the bedrock in the channels. The richest part forms a streak of irregular width referred to in the English colonies as the ‘‘run of gold” and in the United States as the ‘‘pay streak”’ or ‘‘pay lead.” This does not always occupy the deepest depression in the channel and sometimes winds irregularly from one side to the other. It often happens that the values rapidly diminish at the outside of the pay lead, but again the transition to poorer gravel may be very gradual. An exact explanation of the eccentricities of the pay lead may be very difficult to furnish. Its course depends evidently on the prevailing conditions as to velocity of current and quantity of material at the time of concentration. The gravel outside of the ‘“‘pay streak’”’ would ordinarily be regarded as extremely rich by the hydraulic miner, who would be content with a yield of 10 cents a cubic yard; but the drift miner is obliged to leave as unpayable gravel containing from 75 cents to $2 a cubic yard. Figure 12 (p. 151) illustrates the position of the pay lead in the Mayflower channel, according to Ross E. Browne. SIZE OF THE GOLD. Although the larger part of the gold in the channels is fine or moderately fine, large nuggets are sometimes found and much speculation has been indulged in as to their origin. It has been repeatedly stated in the literature that large nuggets occur more commonly in the gravels than in the veins. It is difficult to trace the origin of this tradition; it certainly has little foundation in fact. The largest masses of gold found in California are said to be that from Carson Hill, which weighed 195 pounds troy, and that from the Monumental quartz mine, in Sierra County, which weighed about 100 pounds troy. The mass at Carson Hill, if not directly in a quartz vein, was at any rate immediately below the croppings and not in any well-defined alluvial channel. The well-known heavy nuggets obtained near Columbia, Tuolumne County, were found in a vicinity of rich pocket veins where decay of rocks has proceeded without much interference since Tertiary time, and in which assuredly there has been little transportation. Heavy masses of gold are exceedingly common in the so-called pocket veins of Sonora. Many of the veins near Alleghany and Minnesota, in Sierra County, contain remarkably heavy masses of gold. Hanks,' in his list of nuggets found in California, states that a slab of gold quartz extracted from the Rainbow mine, near the locality just mentioned, was calculated to contain gold to the value of $20,468. The total yield from a single pocket of this mine was $116,337. The Ballarat nuggets, some of which weighed from 100 to 200 pounds, found near the town of Ballarat, in Victoria, Australia, are often quoted as conspicuous examples of masses of gold } Hanks, H. G., Second Rept. State Mineralogist California, 1882, p. 49.