** Morningstar says Pilbara Minerals' PLS.AX mineral resource upgrade at Pilgangoora ops in Western Australia solidifies co's status as one of the largest hard rock lithium miners globally

** Investment research firm says higher lithium oxide grades typically lead to lower unit costs as more lithium is extracted per metric ton of ore

** Attributes miner's last week's gains of 3.2% to increased confidence in resolution of U.S.-China trade dispute

** China is the largest global producer of lithium batteries

** Morningstar keeps fair value estimate at A$3

** Stock has gained over 4.5% so far this week

(Reporting by Kumar Tanishk in Bengaluru)

((Tanishk.Kumar@thomsonreuters.com; X: @thatstanishk http://www.x.com/thatstanishk;))