Short answers, pulled from the story.
The hinge line is the specific curve joining points of maximum curvature on any single folded surface. This line may stretch straight across the rock or follow a gentle arc depending on local stress conditions.
Fold tightness measures the angle between limbs tangential to the folded surface at each inflection line. Gentle folds maintain interlimb angles between 180 degrees and 120 degrees while open ranges span 120 to 70 degrees, close folds occupy the 70 to 30 degree range, and tight folds compress between 30 and 0 degrees.
Box folds appear in the La Herradura Formation within Morro Solar Peru where layered rocks shorten parallel to their own structure. These structures often develop above good detachments found in middle Triassic evaporites within the Jura Mountains.
Mineral veins form because voids between layers trigger mineral deposition when water pressure remains lower inside than outside them. Over millions of years this process gathers trace minerals from vast expanses of rock depositing them at very concentrated sites.
Concentric folds result from warping via active buckling of layers maintaining uniform layer thickness whereas similar folds form through shear flow where layers lack mechanical activity. Similar folds display thinning limbs and thickening hinge zones lacking uniform thickness.