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24-019
Comparative Mineralogy of the 5-Element Arsenide Vein Systems
of the Black Hawk District, Grant County, New Mexico
Jakob Newcomer
New Mexico Tech, Socorro, NM
Virginia T. McLemore
New Mexico Bureau of Geology and Mineral
Resources Socorro, NM
Evan J. Owen
New Mexico Bureau of Geology and Mineral
Resources, Socorro, NM
Zohreh Kazemi Motlagh
New Mexico Tech, Socorro, NM
ABSTRACT
Five-element style deposits are unusual hydrothermal sys-
tems that are typically characterized by a nickel-cobalt-arse-
nic-silver-bismuth metal assemblage. This mineralization
is often represented by abundant native silver, arsenic, or
bismuth, and followed by nickel, cobalt, and iron arse-
nides (skutterudite, safflorite, nickeline, rammelsbergite,
and lollingite). The Black Hawk district in Grant County,
New Mexico is one of the few examples of this mineraliza-
tion style in the United States. Despite the differences in
formation temperature, depth of emplacement, and host
rocks between five-element style deposits worldwide, there
are commonalities in mineralogy, ore texture, and composi-
tion. A detailed exploration of the native metal and arsenide
phases will be performed to compare ore forming fluids
between systems and the effects on styles of mineralization
and paragenesis, as well as to aid in broader classification
of the deposit style. Mineralogy and mineral relationships
of the Black Hawk District and other five-element deposits
worldwide will be characterized by reflected light petrogra-
phy, scanning electron microscopy, X-ray diffraction, and
electron microprobe analysis. Mineralogical phase diagrams
will be generated to better understand the driving processes
and evolution of the systems through native metal and arse-
nide precipitation.
PURPOSE OF STUDY
The purpose of this study is to analyze the five-element vein
deposits of New Mexico’s Black Hawk District in Grant
County by performing detailed mineralogical and chemi-
cal analyses. This unusual type of deposit, being enriched
in nickel, cobalt, silver, and uranium, makes it a target to
explore for critical minerals. A more detailed understanding
of the mineralogy and compositions of the deposit, as com-
pared to other five-element deposits around the world, will
better inform sourcing and production of critical minerals.
Critical minerals of interest from this deposit style include
cobalt, nickel, arsenic, and bismuth.
Five-element deposit types are uncommon around the
world and are unusual in the elements present as well as
the minerals that form (Markl et al., 2016). Typical five-
element deposits contain a silver- nickel-cobalt-arsenic-bis-
muth assemblage, sometimes alongside copper, uranium,
lead, zinc, mercury, and antimony. These often occur as
native silver, bismuth, and arsenic, with minor sulfides, as
well as arsenides of cobalt and nickel. The arsenides are of
particular interest, because previous studies described sev-
eral different mineral species, some of which have since
been discredited, namely smaltite and chloanthite, which
were erroneously determined to be arsenic deficient mem-
bers of the skutterudite group (OEN et al., 1984). These
arsenides have been reported from other deposits to show
chemical zoning of nickel, cobalt, and iron, giving greater
insight into ore fluid evolution.
PREVIOUS STUDIES
Despite the historical and modern importance of this
deposit style, the processes of formation have been poorly
understood. The study by Markl et. al. (2016) attempts to
explain the main formation mechanism of five-element
style deposits. By examining many classical European five-
element deposits, and compiling information on other