See the arrows on the sample in the picture. ginguro bands Abstract: High-grade ore zones in low-sulfidation epithermal deposits are commonly associated
with the occurrence of banded quartz veins. The ore minerals in these veins are heterogeneously
distributed and are mostly confined to ginguro bands, which can be identified in hand specimen
based on their distinct dark gray to black color. Micro-X-ray fluorescence element maps obtained
on representative samples of banded quartz veins show that Au occurs together with Ag minerals
in some of the ginguro bands, but Au can also be present in quartz bands that are light gray to white
and cannot be macroscopically distinguished from barren bands. The occurrence of compositionally
distinct ginguro and gankin bands, the latter being a new term coined here for colloform quartz
bands containing primarily electrum or native gold, can be explained by temporal changes in the
composition of the ore-forming thermal waters or variations in the conditions of ore deposition.
Textural relationships, including the dendritic shape of ore minerals that appear to have grown in
a matrix of silica microspheres, suggest that the ginguro and gankin bands have formed as a result
of rapid deposition associated with vigorous boiling or flashing of the thermal waters. One of the ea
rliest descriptions of these ore bands is given by Mukaiyama [13] for the epithermal ore of the Sado Kinzan deposit in Japan. Ginguro bands have
been described from many other deposits worldwid
e, including Buckskin National in Nevada [14] Minerals 2019, 9, 740 2 of 25 Hokuryu in Japan [15]; Ivanhoe in Nevada [14]; Koryu in Japan [7,12]; Kushikino in Japan [5]; and Midas in Nevada [9]. Some of the best examples of ginguro bands occur at the high-grade Hishikari
deposit of Kyushu in Japan [6,8,10,16,17]. At all of these deposits, ginguro bands are characterized by
extremely high precious metal grades and can contain thousands of ppm Au and Ag. Many low-
sulfidation epithermal deposits would not be economically viable without the occurrence of these
high-grade ore bands [11].