Appendix C. Commodity/Geochemical Index by Paul B. Barton

This file shows economic (or potentially economic) commodities as primary products or by-products; it also indicates geochemical anomalies. These represent the elements present anywhere in the deposit, not solely in haloes distinct from ore. The listing covers only those deposits for which models are present elsewhere in this compilation. Figure 206 is a graphical presentation of some of the information in the following table. It provides an overview of the distribution of the elements among deposit types.

In an effort to represent the commonness or rarity of features, numbers are assigned. Universally present products/anomalies rate a +5 (shown simply as “5”) grading down through 0 to -5 (shown as "(-5)” ) in a system similar to PROSPECTOR. The “0” value will seldom, if ever, be shown as it is the "don't know" (or "don't care") default. Note that negative numbers for "Primary" or "By-product" are not used, although they might be applied to indicate serious deleterious elements, such as phosphorus in iron ores. In almost all instances at present, these values will be guesses based on experience, not hard data; however, we do urge the compilation of data to make such assignments possible eventually. It is our intent to have the “1”, “2”, “3", “4”, and “5” scores correspond respectively to the 0-10, 10-30, 30-70, 70-90, and 90-100 percent frequency relationship between the element and the deposit type. Obviously such statistical approaches are meaningless for deposit types having few representatives, such as emerald veins (31c), but the value can still be useful as an estimate of the compiler's opinion regarding the probable generality of the observation. The abbreviated suffixes “(prox.)" and “(dist.)" indicate respectively proximal (or nearer source) and distal (or farther from the source). For more complex relations please refer back to the models.

Figure 206 shows only the presence of an element at some unspecified anomalous level, either proximally or distally with respect to the deposit. The elements are grouped in such a way that the distinction between those of granitic and mafic associations can be easily made. The elements of high mobility in hydrothermal environments form a distinct grouping on the right side of the matrix.

It should be obvious from examination of the table and figure below that the presence of a given element seldom, if ever, "proves" the existence of an ore deposit. Anomalous amounts of some elements such as copper, gold, iron, and zinc are so common in so many settings that their presence tells very little about the possible character of the host deposit. Their presence is encouraging, however, and indicates that additional studies may be warranted.

Figure 206a. [Left side of ] Matrix diagram showing deposit models and their geochemical signature. [Black] closed and [red closed] circles indicate that the element is anomalous proximally or distally to the deposit, respectively.

Figure 206b. [Right side of ] Matrix diagram showing deposit models and their geochemical signature. [Black] closed and [red closed] circles indicate that the element is anomalous proximally or distally to the deposit, respectively.