The term 'en echelon' refers to closely-spaced, parallel or subparallel, overlapping or step-like minor structural features in rock (faults, tension fractures), which lie oblique to the overall structural trend. Conjugate deformation structures are related in deformational origin.
Magmatic enclaves are volumes of rock surrounded by emplaced host rock of related but distinct composition and of separated genesis (incomplete magmatic mixing).
Enclaves are distinguished from xenoliths, which are fragments of metamorphically altered older country rock that fell into magma or lava and became enveloped within igneous rock. Enclaves are also distinguished from schlieren, which are concentrations of mafic material that have crystallized out of a single magma.
Microgranitic (mafic) enclaves are common components of plutonic bodies and may represent the result of mingling of mafic and felsic magmas. These enclaves are often ellipsoidal or elongate in shape.
evidence that suggests that prior to incorporation of parent magma globules into the host magma (during magma mingling), the enclaves underwent magma mixing, in a setting where the mafic magma was more abundant than the felsic magma.
Most epithermal ("shallow heat") deposits occur in veins, irregular branching fissures, stockworks, or breccia pipes. Colloform and replacement textures are sometimes recognized, but the majority of epithermal deposits are characterized by open space filling textures (crustification, comb structures, symmetrical banding).
Many epithermal deposits appear to be spatially associated with hot springs and geysers, and these hydrothermal systems may be considered the surface expression of epithermal systems. Alteration of wall rock is predominantly argillic and is accompanied by silicification. Epithelial deposits are commonly associated with large gossans, which are intensely oxidized, weathered, or decomposed rocks that usually form the exposed, upper portions of ore deposits or mineral veins. Common gangue (waste) minerals in the tailings include: quartz, calcite, fluorite, barite, chalcedony, rhodochrosite and dolomite.
Epithermal deposits include a wide variety of ores: Au, Au-Ag, Ag, Pb, Zn, Cu, Sn, Sb, U and Hg.