Half Zantop's interest in Fresnillo, the world's largest and richest silver mining district, began in the mid 1980's. He realised the importance of the district and began, along with his graduate and undergraduate students, investigating the physical and chemical processes of ore formation through geological and geochemical research. Fresnillo is located in Zacatecas state 750 km NW from Mexico City. A series of epithermal veins and replacement bodies are hosted in Cretaceous sedimentary and mafic volcanic rocks.

From the mid-1980's to 2001, Half supervised 10 thesis projects at Fresnillo, as well as conducting his own research. Initial research in the district began with a study on the geology and geochemistry of the Santo Nino vein by Bruce Gemmell (PhD, 1986) and a study on selected veins in the central part of the district by Eduardo Chico (MSc, 1986). Laurie Benton (Hons, 1987) undertook project investigating the trace element and strontium isotope compositions of the calcite of the Santo Nino vein. Janice Gardner (MSc, 1987) compared hand-held and Landsat remote sensing data for rocks and hydrothermal alteration in the district. John Lucio (MSc, 1990) investigated the Pb and Sr isotopes of ores and host rocks throughout the district. Michael McDougall (Hons, 1998) completed a Honors thesis which included a district-scale geochemical study, including pathfinder elements. Charles Lalanne (Hons, 1998) investigated the residence and depositional mechanisms of gold in the San Mateo and San Carlos veins. Edward Hughley (Hons, 1999) undertook a study of the mineral deposition, paragenesis and fluid flow in the San Carlos vein. A fluid inclusion and catholuminescence study of the Santo Nino and San Carlos vein systems was done by Eric Eckberg (Hons, 1999). Jennifer Flight (Hons, 2001) inferred the presence of ore at depth throughout the district via a comparison of oxygen isotope compositions and fluid inclusion temperatures at surface.

At the time of his death, Half was planning to combine existing data with new field and laboratory work in order to develop an ore-forming hypothesis and model for the whole district. Half and Susanne will be sorely missed by all their students, colleagues and friends.