Members of our Inner Circle service often ask for our portfolio investing advice on stocks they are thinking of buying that we don’t cover in our newsletters. These companies range from the most speculative penny mines to large multinational corporations.

Many of these stocks fall into a grey area. Sometimes our advice is that they are “okay to hold,” but we wouldn’t recommend them for new portfolio investing. When Inner Circle members ask about one of these companies, that’s what our advice would be: it’s “okay to hold.” But when they ask about companies we don’t recommend, we say so.

Here are three recent examples from our Inner Circle portfolio investing advice. One is a gold miner that could be on the verge of breathing new life into an old mine, another is a real-estate investment trust that’s overly concentrated in western Canada, and the third is a technology firm that aims to develop a safety-monitoring system for airliners.

Trelawney Mining and Exploration (symbol TRR on Toronto), owns three gold properties that are located halfway between the northern Ontario cities of Timmins and Sudbury. The properties centre on the Chester mine, which was nearly completed in the 1980s, but never went into production.

In early March 2010, Trelawney’s shares jumped from $0.60 to as high as $1.35. That’s when the company reported results from its latest drilling at Chester, which it conducted to see how much gold is beyond the known deposits. The drilling results included 107.11 metres of a high 8.20 grams per tonne of gold, including 313.55 grams per tonne over 2.56 metres.

Trelawney took advantage of the price rise to issue 14.2 million shares at $1.05 each. That raised $14.9 million, which the company will use to continue its exploration program at Chester.

Our portfolio investing advice: To make the Chester mine attractive, Trelawney needs gold prices to remain high. But the existing infrastructure and the 269,300-ounce resource base already established at the mine give it appeal. Trelawney is okay to hold, but only for highly aggressive investors.

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Artis REIT (symbol AX.UN on Toronto), is a real estate investment trust that owns industrial, office and retail properties in western Canada.

Artis continues to grow by acquisition. It recently bought a number of new properties in western Canada, including four in Alberta. The new properties will increase the company’s leasable space to 8.4 million square feet in 105 properties. Geographically, its leasable space breaks down as follows: Alberta (49.7%), Manitoba (31.6%), B.C. (11.0%) and Saskatchewan (7.7%).

The company’s largest corporate tenants include TransAlta, Sobeys, Shoppers Drug Mart, MTS Allstream and Bell Canada. Other major tenants include the federal government and the provincial governments of Alberta, Saskatchewan and Manitoba.

Artis pays a monthly distribution of $0.09 per unit. The annual rate of $1.08 yields 9.8%.

Our portfolio investing advice: Artis’s high yield gives it some appeal, but its concentration in western Canada adds risk. Focusing on any one province or region is more speculative than spreading out across the country. That’s especially true in western Canada, which depends more on high commodity prices than other parts of the country. The company’s growth-by-acquisition strategy also adds risk. We don’t recommend Artis REIT.

Star Navigation Systems Group (symbol SNA on Toronto), is developing a safety-monitoring system for airliners. Star’s technology collects and records flight data as it happens, and relays it to the company that owns the aircraft.

Star has sold few of its systems to date, and none to major airlines. In the three months ended March 31, 2010, its revenue was $75,660 compared to $196,503 a year earlier. The company lost $821,402, or $0.01 per share, in the latest quarter. A year earlier, it lost $490,606, or $0.01.

Star operates in a narrow and competitive market. To be successful, it will need to keep increasing its marketing and research spending: In the latest quarter, it spent $288,398 on these activities, up 44.7% from $199,254 a year earlier.

Our portfolio investing advice: Even if Star’s safety systems had substantial advantages over current systems, it would face a huge challenge to persuade doubtful purchasing agents to buy. Judging by revenue achieved to date, it doesn’t seem to have made any progress in that area. We don’t recommend Star Navigation.

If you have investment-related questions, or if you’d like to ask me about stocks you’re considering buying (or selling), you should join my Inner Circle service. Click here to learn more.