Should you buy these London stocks after today's updates?

Shares in oil explorer TheParkmead Group (LSE: PMG) have galloped 6% higher in mid-week trade after the announcement of exciting asset news.

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Parkmead has doubled its holding in the Polecat and Marten oilfields in the North Sea, sites that are within spitting distance of the Buzzard field. The oilie describes the assets as "two sizeable existing Buzzard sandstone oil accumulations, which are jointly estimated to hold over 90m barrels of oil in place and over 33m barrels of contingent resources."

Parkmead's increased stake has boosted its total contingent resources by 39%, to 59.1m barrels of oil equivalent. And the proximity of Polecat and Marten to the firm's Perth-Dolphin-Lowlander (or PDL) hub project means that "they could be jointly developed as part of the Greater PDL Area project," Parkmead noted.

While exciting news, I still believe Parkmead is an unsuitable stock pick for risk-averse investors.

The company is expected to remain lossmaking until 2017 at least, and given the heavy supply imbalance washing over the oil market -- not to mention the unpredictability of Parkmead's operations -- I believe earnings could drag long into the future.

Big beast

Real estate investment trust (or REIT) Tritax Big Box(LSE: BBOX) was also heading higher following news of another acquisition.

Shares have touched fresh record peaks above 140p per share following news that Tritax had bought Amazon's distribution centre at Kingston Park, Peterborough for £42.9m. This is the first property Tritax has let to the US internet giant, and takes the British company's portfolio to 31 'big box' assets.

Today's announcement follows hot on the heels of another acquisition, Tritax saying on Tuesday that it had snapped up the distribution hub of Kellogg's in Trafford Park, Manchester for £23.5m.

While the full impact of Brexit on the UK economy is yet to be fully understood, I believe Tritax's bias towards blue chip tenants should allow it to navigate any near-term shocks in the UK economy.

And I reckon a forward P/E ratio of 15 times and 4.5% dividend yield make Tritax an attractive pick at current prices.

Losing its shine

The news isn't so good over at Gem Diamonds(LSE: GEMD), however, a disappointing operating update sending the stock 3% lower from Tuesday's close.

Gem Diamonds announced that "excessive snow falls and severe winds" across the Maluti Mountains in Lesotho, South Africa have affected access to its Letseng mine. The company is using standby generators due to damage to power lines, resulting in reduced production rates, although electricity supply is expected to be fully restored in the short term.

As a result, Gem Diamonds said that "full year guidance for ore tonnes treated and operating costs may need to be re-assessed," although it added that the strong operational performance during January-June means that "carats recovered are not expected to be affected materially."

Today's news adds another layer of risk to Gem Diamonds, the company already battling against a backdrop of subdued stone diamonds thanks to plentiful supplies. I reckon investors should continue to steer clear despite a 'low' forward P/E rating of 7.4 times.

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Royston Wild has no position in any shares mentioned. The Motley Fool UK owns shares of and has recommended Amazon.com. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.