Ann: Oman Drillng Update, page-60

Yes the words massive and supergene sometimes are not the deciding factors sometimes have to delve a bit deeper .
My understanding is supergene (enrichment ) is when minerals present seep down in the earth to a hard pan in the soil where they concentrate in a horizontal layer (tabular) causing a higher grade to be there. The opposite of a horizontal layer is a vertical layer of minerals (a dike) trapped between country rock as would happen with a fault .
The dikes structure is normally more economic to mine and has less overburden to remove and may also be exposed at surface plus the excavator bucket is not diluting the ore as much with each scoop and less overbreak from blasting .
In UG mining the dike structure leads itself to cut and fill mining so a ready made platform keeps being made for the miner .
Similar situation between massive and disseminated ore may be higher grade insitu with massive but also more dilution which is ultimately reflected in the reserve grade in this case it is shown in your chart as reserve (measured) for the massive ore so dillution is taken into account but only as indicated for the supergene ,.
I suspect that supergene ore will fall in grade once it goes into the measured category due to the above explained rational for supergene .
Welcome to be corrected by a geo or mine engineer which I am not .