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The Tertiary Gravels of the Sierra Nevada of California - Introduction

Any serious attempts to “discover” the real value of Original Sixteen to One Mine must include at least a cursory reading of Waldemar Lindgren’s epic professional paper, the Tertiary Gravels of the Sierra Nevada of California.

Here are some excerpts from the introduction.

 

Under the initial eyes of the Department of the Interior, United States Geological Survey, Waldemar published Professional Paper 73 in 1911. To many, 1911, represents the historical past. To California gold miners, it is an important part of the story of gold with present day implications. Does anyone believe all the placer and lode gold deposited in the Sierra Nevada is gone? NO. Just how much remains buried in one of the World’s richest gold belts, continues to be the topic for discussion.

Lindgren’s introduction reads like fine prose, not like the dry reports written by later day geologists. Excerpts follow. See for yourself. Lindgren provides us “The Big Picture” unconfused by the clutter of self serving details in evaluating the current potential of the Sixteen to One vein system.

 

THE TERTIARY GRAVELS OF THE SIERRA NEVADA OF CALIFORNIA.

By: Waldemar Lindgren

INTRODUCTION

OUTLINE OF LATER GEOLOGIC HISTORY OF THE SIERRA NEVADA

This report attempts to trace a part of the history of the Sierra Nevada, the great range which, for 300 miles, divides the central valleys of California from the deserts of the Great Basin. It presents an account of the Tertiary formations of the range and deals especially with the origin and distribution of the gold-bearing gravels, which made these mountains one of the treasure houses of the world.

The Paleozoic and early Mesozoic seas once extended over the site where the Sierra now lifts its broad back. Toward the close of the Mesozoic era the sediments were compressed in heavy folds, and the intrusion of granitic magmas forced them upward to lofty summits. After the intrusion, the fissures and joints of granitic rocks and altered sediments became filled with veins and seams of gold-bearing quartz. A long period of erosion in the early Cretaceous planed down the newborn mountains. The concentration of the gold from the veins began in countless streams. Pauses in the erosion, when the topography had been reduced to gentle outlines, permitted deep rock decay and promoted the liberation of gold from its matrix. Renewed uplift quickened erosion and facilitated the further concentration of gold. Throughout Cretaceous and Tertiary time these conditions continued.

Long-quiescent volcanic forces asserted themselves toward the end of Tertiary time, contemporaneously with the greatest volcanic activity in the Great Basin. Rhyolite flows filled the valleys, covered the auriferous gravels, and outlined new stream courses in the old valleys. Eruptions of andesitic tuffs began in enormous volume and effectually buried a large number of the streams, filling their valleys to the rims. At the close of the Tertiary period a steaming, desolate expanse of volcanic mud covered almost the whole of the northern Sierra, in startling contrast to the peaceable verdure-clad hills of the Miocene. Wherever the canyon-cutting streams destroyed the old channels, the gold in those channels became concentrated in the canyons and thousands of disintegrated quartz veins added to the previous concentrates.

The barren lava flows and the canyon slopes again became clothed by vegetation, this time of the type belonging to a cooler but still temperate climate.

During the last brief span of a few thousand years the Sierra Nevada has remained as we now see it, with the pleasing oak groves of the foothills, the somber giant pines of the middle slopes, and the storm-scarred hemlocks of the summit ridges.

The peace of the wilderness was interrupted in 1849. An army of gold seekers invaded the mountains; at first they attacked the auriferous gravels of the present streams, but gradually the metal was traced to the old Tertiary river beds on the summits of the ridges and to the quartz veins, the primary source of all the gold in the Sierra Nevada. The Tertiary stream beds- the “channels,” as they are called-proved rich but difficult to mine. New methods were devised; by hydraulic mining the gravel banks were washed down by the aid of powerful streams of water, and by drift mining the bottoms of the old streams beds were followed by tunnels underneath the heavy volcanic covering.

Millions of dollars were annually recovered from these Tertiary channels, and the heyday of this industry fell in the seventies of the last century. Since then, owing to the prohibition of hydraulic mining and the gradual exhaustion of the richer channels suitable for drift mining, the industry has slowly decayed until in the year 1908, the total production of the drift, hydraulic, and surface mines of the range, for the first time since 1848, fell below $1,000,000; indeed, this figure also includes the value of the gold washed from Quaternary gravels along the rivers. Gold is still contained in the Tertiary channels; miles of them are still unworked; but the problems are how to extract it without damage to other property from the debris and how to reduce the cost of drift mining so as to permit the exploitation of the less remunerative deep gravels.

 

 

GEOGRAPHIC DISTRIBUTION

The occurrence of gold in paying quantities in the Tertiary gravels of the Sierra Nevada is limited almost entirely to the gravels in which quartz and metamorphic rocks form the principal components. This is natural because the gold is derived wholly from veins occurring in the metamorphic rocks of the range.

In Sierra, Yuba, and Butte counties the Tertiary channels are rich in gold almost up to the divide of the range. Wherever the channels cross-areas rich in quartz veins, they become heavily charged with gold.

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. 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.

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 the 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, directly in quartz vein, was at any rate immediately below the croppings and not in any well defined alluvial channel. Heavy masses of gold are exceedingly common in the so-called pocket veins. 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 mine2, 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.

ACKNOWLEDGEMENTS

The work of the United States Geological Survey in the gold belt of California began in 1886 and was concluded about 15 years later. The examinations were began by Mr. H. W. Turner and the author under the direction of Mr. G. F. Becker (from 1886 to 1892).

A considerable part of the study of the Tertiary gravels of the Sierra has fallen to the lot of the author because the most important gravel-mining districts were located in the area assigned to him. He has also at various times visited the principal districts outside of his area.

Heartiest thanks are extended to the many mining men who, by information and advice, have facilitated the collection of this data

 
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