adams] ZINC AND LEAD DEPOSITS OF NORTHERN ARKANSAS. 11)5 
honeycombed appearance. The richer deposits appear to be related 
to fracture zones, and occur along the fissures and replacing the 
adjacent rocks. The path of the ore-bearing solutions in descending 
has apparently been along fractures and laterally along the bedding 
planes, and the mineralization decreases away from the fracture zone. 
Sulphide deposits in bedded breccias. — In the brecciated beds of the 
Ordovician dolomites the open spaces between the fragments have 
afforded channels for the ore-bearing solutions, and the precipitation 
of the sulphides and dolomite or pink spar has usually taken place 
without the dissolving of the country rock to any appreciable extent. 
The pink spar is not always accompanied by ore. The sulphides have 
been deposited in a somewhat local way, many factors being con- 
cerned. Not infrequently, in prospecting, breccias containing pink 
spar and but little ore are found; and, where the breccias are ore bear- 
ing, when they are followed for a considerable distance they usually 
show a decrease in the amount of ore. 
Sulphide deposits in fissures. — In the Mississippian limestones most 
of the mines and prospects are related to fissures, the ore occurring 
in material filling the fissures or in the fissure and the openings adja- 
cent to it. These deposits differ from those in the fractured dolomites 
in being more clearly defined. The gangue is usually secondary chert 
and calcite. The walls of the fissures exhibit slickensiding, as a 
result of the movement of beds, and frequently indicate displacement 
in a horizontal direction. 
Sulphide deposits in fault breccias. — Where the Mississippian lime- 
stones have been displaced by normal faulting and the rocks have 
been dragged, they not infrequently exhibit brecciation. The angular 
fragments are largely primary chert, and the ore occurs associated 
with a calcareous and siliceous matrix which cements the breccia. 
Sulphide ore in country rock. — In many of the mines and prospects 
the country rock has not been mineralized. In other cases, for a 
short distance adjacent to fissures, fractures, and water channels, the 
ore-bearing solutions have formed what is here called accessory ore. 
The action in this case has been one of replacement. The country 
rock exhibits recrystallization and carries small crystals of ore. 
Where accessory ore is found the main ore body is usually rich, and 
there is a suggestion that deposition in the country rock resulted 
because of the large amount of ore in solution at these places. In the 
northern Arkansas district the scattered crystals of blende in the 
country rock are spoken of as disseminated ore. This term, unfortu- 
nately, is not quite appropriate, and, accordingly, the word accessory 
is suggested, since it does not imply the mode of deposition usually 
ascribed to disseminated ores. Accessory ore, inasmuch as it is usu- 
ally found associated with rich ore bodies, is looked upon by the pros- 
pectors as a favorable indication. The ore in secondary chert is not 
included under this head. 
