"Aquaclude" may be an obsolete term; I seem to remember reading somewhere that there is another term that's preferred now, but I don't remeber what it is. Basically, as I learned it 30-some years ago, an aquaclude is an impermeable layer, through which ground water travels poorly, or not at all. In the photo, that darker streak is a dike that appears to have confined groundwater seepage to the lower right. Note that in the upper left, there are no stalactites or flowstone. The nature of the dike is unclear to me... I know on previous tours, it has been described as a clastic dike. Unconsolidated sediment intruding up into this limestone prior to metamorphosis seems like a possibility, but post-metamorphic intrusion seems unlikely. Everything else in the neighborhood would also be metamorphosed. However, on this trip, it was described as an igneous intrusion, which makes somewhat more sense in this setting. But I couldn't get at it, and the powers that be would certainly not condone taking a sample for closer inspection in better light. So from my perspective, I'll just leave the question as unsettled. Below is an annotated version of the photo, with the dike highlighted, and ovals around areas with obvious speleothems.
Photo unmodified. May 9, 2013. FlashEarth Location. (Since we're underground, I have only a vague idea where this is with respect to the surface.)